ghc-toolchain: Check for C99 support with -std=c99
Previously we failed to try enabling C99 support with -std=c99, as
autoconf attempts. This broke on older compilers (e.g. CentOS 7) which
don't enable C99 by default.
Fixes #23879 (closed).
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Previously we failed to try enabling C99 support with -std=c99, as
autoconf attempts. This broke on older compilers (e.g. CentOS 7) which
don't enable C99 by default.
Fixes #23879 (closed).