Fix compiler pragma warning on GCC <= 4.2

[prpr19xx]

I get this error on GCC 4.5.2:
curl_setup.h:37: warning: unknown option after '#pragma GCC diagnostic' kind

I don't known which version implemented this, possibly 4.6, but just rule out any 4.x version, which is probably good enough.

[testclutch]

Analysis of PR #16152 at 9c90db75:

Test http/test_14_auth.py::TestAuth::test_14_03_digest_put_auth[h3] failed, which has NOT been flaky recently, so there could be a real issue in this PR.

Generated by Testclutch

[vszakats]

This pragma works without warning in 4.4.0 according to a recent CeGCC port #16062. This is confirmed by godbolt.org with 4.4.7.

More details here: https://gcc.gnu.org/legacy-ml/gcc-help/2011-01/msg00113.html

Can you share your command-line, platform and other details to replicate this?

[prpr19xx]

Sorry, I've got my version numbers mixed up. The cross-compiler used is 4.2.0. Here's some test case output:

$ cat gcctest.c
#pragma GCC diagnostic ignored "-Wsign-conversion"

int main(void)
{
    return 0;
}

$ mipsel-linux-gcc -c gcctest.c
gcctest.c:1: warning: unknown option after '#pragma GCC diagnostic' kind

$ mipsel-linux-gcc -v
Using built-in specs.
Target: mipsel-linux-uclibc
Configured with: ../gcc-4.2.0-20070124/configure --prefix=/opt/toolchains/crosstools_hf-linux-2.6.18.0_gcc-4.2-11ts_uclibc-nptl-0.9.29-20070423_20090508/ --build=mipsel-linux --host=mipsel-linux --target=mipsel-linux-uclibc --with-build-sysroot=/usr/src/redhat/BUILD/build_uClibc --enable-languages=c,c++ --disable-__cxa_atexit --enable-target-optspace --with-gnu-ld --with-float=hard --enable-threads --infodir=/opt/toolchains/crosstools_hf-linux-2.6.18.0_gcc-4.2-11ts_uclibc-nptl-0.9.29-20070423_20090508/info --mandir=/opt/toolchains/crosstools_hf-linux-2.6.18.0_gcc-4.2-11ts_uclibc-nptl-0.9.29-20070423_20090508/man --with-arch=mips32 --disable-libmudflap --disable-nls --with-gnu-plts
Thread model: posix
gcc version 4.2.0 20070124 (prerelease) - BRCM 11ts-20090508

[vszakats]

There are more places in the code that may hit such pragma.
IMO we should either address them all, or draw a limit for legacy gcc
version support. Addressing them brings up the issue of how to make
tests with such old version. 4.2 was released in 2007.

[vszakats]

@prpr19xx I created #16157 which deletes the code that created this problem.
Can you re-test and tell if it fixes it for you?

[prpr19xx]

@vszakats Yes #16157 works fine for me, thanks.

[vszakats]

Note for future ref.: This is 4.2.0 pre-release. 4.2.0 stable does support this pragma.

[vszakats]

Thanks @prpr19xx for your patch and reports. Merged #16157, and this should now be fixed.