Currently, it is only tried by two places:
(1) place using prefix
(2) system place by gcc -print-file-name=crt1.o
But it is possible to have different prefix (like make distcheck time).
We should try more places to find it:
(3) $prefix-of-gpgrt-config/lib/pkg-config
(4) $prefix-of-gpgrt-config/lib/$host-triplet/pkg-config
Considered again, I realized that (1) is no need to check.
$host-triplet is the one of Debian style.
We need to check libdir like /usr/lib32 or /usr/lib64 style one of Fedora/openSUSE.
For other libraries, like libgcrypt, it is mostly OK with old gpg-error.m4, because those libraries don't depend on new libgpg-error features.
But for the specific case when there is older libgpg-error (for particular library build) in /usr/local and newer one in system, user may encounter problem after its installation. Build goes success with newer system one, but runtime uses /usr/local.
To solve this issue, gpg-error.m4 in those libraries should be also updated to detect older libgpg-error in /usr/local.
We also need to support the use case of GNU cross style, like when we build with MinGW toolchain.
I found that the use of $CC -print-file-name=crt1.o won't work with some cross compiler.
For example, on my system of Debian bullseye for cross compiler ppc64el, while it's for multiarch configuration, crt1.o is under GNU cross style directory: /usr/powerpc64le-linux-gnu/lib
Use of $CC --print-search-dirs is more reliable.