GHA/http3-linux: add CI reproducer for --with-ngtcp2=<path> regression

[vszakats]

Configure LibreSSL autotools job with --with-ngtcp=<path> instead of
adding ngtcp2 to PKG_CONFIG_PATH. To test this way of configuration in
CI and test for the regression reported in #20889.

Turns out this way of configuration isn't affected by the detection
issue in this particular case.

It also works for other backends except for these two, subject to
separate fixes:

• BoringSSL fix: boringssl: Remove openssl from Requires.private ngtcp2/ngtcp2#2070
• GnuTLS fix and BoringSSL workaround: configure: fix --with-ngtcp2=<path> option for crypto libs #20920

Follow-up to 666db80 #20891
Follow-up to 8db0e28 #18189
Follow-up to 9950066 #18028 #18022

---

• move configure pkg-config trace feature to sep PR, and rebase on. → configure: add option to trace pkg-config detection details #20931

---

• Tested OK with current master: https://github.com/curl/curl/actions/runs/23112010665/job/67131008707?pr=20926
• build: regression LibreSSL native crypto lib with ngtcp2 1.15.0+ #20889 error reproduces with the fix reverted: https://github.com/curl/curl/actions/runs/23112334831/job/67131894726?pr=20926#step:18:310
• pkg-config trace feature tests in all AM jobs:
  H3 Linux: https://github.com/curl/curl/actions/runs/23121500311/job/67156293555?pr=20926#step:18:330 (fail, pkgconf)
  Linux: https://github.com/curl/curl/actions/runs/23121500329/job/67156283850?pr=20926#step:39:232 (slackware is pkg-config)
  Windows: https://github.com/curl/curl/actions/runs/23120741088/job/67154236531?pr=20926
  Old Linux: https://github.com/curl/curl/actions/runs/23121500323/job/67156272080?pr=20926#step:21:224 (pkg-config)
  non-native: https://github.com/curl/curl/actions/runs/23120741100/job/67154216142?pr=20926
  H3 Linux: https://github.com/curl/curl/actions/runs/23120741073/job/67154235113?pr=20926
  Linux: https://github.com/curl/curl/actions/runs/23121129085/job/67155256452?pr=20926 (pkg-config all lines)
  Old Linux: https://github.com/curl/curl/actions/runs/23121129078/job/67155255953?pr=20926#step:21:203 (pkg-config all lines)

[vszakats]

BoringSSL job doesn't like --with=ngtcp2=:
https://github.com/curl/curl/actions/runs/23112528016/job/67132417724?pr=20926

[vszakats]

After a few many hours more on this, BoringSSL also fails with --with-ngtcp2=<path>.
In this case it isn't a curl issue, but rather an ngtcp2 or BoringSSL one:
BoringSSL does NOT provide .pc files, yet ngtcp2_crypto_boringssl.pc
lists it as a dependency. Then when correctly pointing to a BoringSSL install
prefix (e.g. via PKG_CONFIG_PATH), there won't there be one. To make it
work, pkg-config must instead find an unrelated openssl.pc!

To make this even more confusing AWS-LC does provide an openssl.pc, and
it also uses ngtcp2_crypto_boringssl as a crypto lib name in ngtcp2. It means
that even though the lib itself is compatible (for now, possibly) with both BoringSSL
and AWS-LC, its .pc file is incompatible for BoringSSL, and requires AWS-LC
(or a fake/surrogate openssl.pc).

[vszakats]

after:

pkgconf, fail:

checking for libngtcp2_crypto_boringssl options with pkg-config... no
configure: pkg-config --exists libngtcp2_crypto_boringssl trace:
---- begin
trying path: /home/runner/nghttp3/build/lib/pkgconfig for libngtcp2_crypto_boringssl
trying path: /home/runner/ngtcp2-boringssl/build/lib/pkgconfig for libngtcp2_crypto_boringssl
trying path: /home/runner/nghttp3/build/lib/pkgconfig for libngtcp2
trying path: /home/runner/ngtcp2-boringssl/build/lib/pkgconfig for libngtcp2
trying path: /home/runner/nghttp3/build/lib/pkgconfig for openssl
trying path: /home/runner/ngtcp2-boringssl/build/lib/pkgconfig for openssl
trying path: /home/runner/nghttp2/build/lib/pkgconfig for openssl
==== error:
Package openssl was not found in the pkg-config search path.
Perhaps you should add the directory containing `openssl.pc'
to the PKG_CONFIG_PATH environment variable
Package 'openssl', required by 'libngtcp2_crypto_boringssl', not found
---- end
configure: error: --with-ngtcp2 was specified but could not find ngtcp2_crypto_boringssl pkg-config file.

https://github.com/curl/curl/actions/runs/23121500311/job/67156293555?pr=20926#step:18:328

pkgconf, fail:

checking for libidn2 options with pkg-config... no
configure: pkg-config --exists libidn2 trace:
---- begin
trying path: /usr/lib/x86_64-linux-gnu/pkgconfig for libidn2
trying path: /usr/lib/pkgconfig for libidn2
trying path: /usr/share/pkgconfig for libidn2
==== error:
Package libidn2 was not found in the pkg-config search path.
Perhaps you should add the directory containing `libidn2.pc'
to the PKG_CONFIG_PATH environment variable
Package 'libidn2', required by 'virtual:world', not found
---- end

https://github.com/curl/curl/actions/runs/23121500329/job/67156283797?pr=20926#step:38:302

pkgconf, success:

checking for openssl options with pkg-config... found
configure: pkg-config --exists openssl trace:
---- begin
trying path: /home/runner/awslc/lib/pkgconfig for openssl
trying path: /home/runner/awslc/lib/pkgconfig for libssl
trying path: /home/runner/awslc/lib/pkgconfig for libcrypto
---- end

https://github.com/curl/curl/actions/runs/23121500329/job/67156283797?pr=20926#step:38:251

pkg-config, fail:

checking for libidn2 options with pkg-config... no
configure: pkg-config --exists libidn2 trace:
---- begin
Cannot open directory #1 '/usr/local/lib/x86_64-linux-gnu/pkgconfig' in package search path: No such file or directory
Scanning directory #2 '/usr/local/lib/pkgconfig'
Cannot open directory #3 '/usr/local/share/pkgconfig' in package search path: No such file or directory
Scanning directory #4 '/usr/lib/x86_64-linux-gnu/pkgconfig'
Scanning directory #5 '/usr/lib/pkgconfig'
Scanning directory #6 '/usr/share/pkgconfig'
Looking for package 'libidn2'
Looking for package 'libidn2-uninstalled'
==== error:
Package libidn2 was not found in the pkg-config search path.
Perhaps you should add the directory containing `libidn2.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libidn2' found
---- end

https://github.com/curl/curl/actions/runs/23121500323/job/67156272080?pr=20926#step:21:347

pkg-config, success:

checking for libpsl options with pkg-config... found
configure: pkg-config --exists libpsl trace:
---- begin
Cannot open directory #1 '/usr/local/lib/x86_64-linux-gnu/pkgconfig' in package search path: No such file or directory
Scanning directory #2 '/usr/local/lib/pkgconfig'
Cannot open directory #3 '/usr/local/share/pkgconfig' in package search path: No such file or directory
Scanning directory #4 '/usr/lib/x86_64-linux-gnu/pkgconfig'
Scanning directory #5 '/usr/lib/pkgconfig'
Scanning directory #6 '/usr/share/pkgconfig'
Looking for package 'libpsl'
Looking for package 'libpsl-uninstalled'
---- end

https://github.com/curl/curl/actions/runs/23121500323/job/67156272080?pr=20926#step:21:291