The ngtcp2-gnutls CI build is broken

[bagder]

See build log from current master. It has been broken for a while now (a few days?)

The curl configure output ends like this:

checking for pkg-config... (cached) /usr/bin/pkg-config
checking for libnghttp2 options with pkg-config... found
configure: -l is -lnghttp2
configure: -I is -I/usr/local/include
configure: -L is -L/usr/local/lib
checking for nghttp2_session_set_local_window_size in -lnghttp2... yes
checking nghttp2/nghttp2.h usability... yes
checking nghttp2/nghttp2.h presence... yes
checking for nghttp2/nghttp2.h... yes
checking for pkg-config... (cached) /usr/bin/pkg-config
checking for libngtcp2 options with pkg-config... found
configure: -l is -lngtcp2
configure: -I is -I/home/travis/ngbuild/include
configure: -L is -L/home/travis/ngbuild/lib
checking for ngtcp2_conn_client_new in -lngtcp2... yes
checking ngtcp2/ngtcp2.h usability... yes
checking ngtcp2/ngtcp2.h presence... yes
checking for ngtcp2/ngtcp2.h... yes
configure: Added /home/travis/ngbuild/lib to CURL_LIBRARY_PATH
checking for pkg-config... (cached) /usr/bin/pkg-config
checking for libngtcp2_crypto_gnutls options with pkg-config... no
configure: error: --with-ngtcp2 was specified but could not find ngtcp2_crypto_gnutls pkg-config file.

[bagder]

@ueno, any idea what it is?