[php-src] Issue #14284: Can't cross-compile with external libcrypt

Issue: https://github.com/php/php-src/issues/14284 Author: orlitzky ### Description At https://bugs.gentoo.org/931884 we have a bug report that boils down to the external libcrypt (./configure --with-external-libcrypt) checks running e.g. ```m4 AC_CACHE_CHECK(for extended DES crypt, ac_cv_crypt_ext_des,[ AC_RUN_IFELSE([AC_LANG_SOURCE([[ ... ]]) ],[ ac_cv_crypt_ext_des=yes ],[ ac_cv_crypt_ext_des=no ],[ ac_cv_crypt_ext_des=no ]) ]) ``` where the last case is executed for cross-compiles and forces the feature to undetected (which, in this case, is fatal). We have a few options to work around this within Gentoo, but I thought it was worth asking about upstream approach more generally. AC_RUN_IFELSE is used in a few places, and I think it would be better if the cross-compile branch were kept consistent to whatever extent that's possible. For another example, take ext/iconv/config.m4: ```m4 AC_MSG_CHECKING([if iconv supports errno]) AC_RUN_IFELSE(... [ AC_MSG_RESULT(yes, cross-compiling) ]) ``` Or ext/pcre/config0.m4: ```m4 AC_CACHE_CHECK([for JIT support in PCRE2], ac_cv_have_pcre2_jit, [ AC_RUN_IFELSE(... [ AC_CANONICAL_HOST case $host_cpu in arm*|i[[34567]]86|x86_64|mips*|powerpc*|sparc) ac_cv_have_pcre2_jit=yes ;; *) ac_cv_have_pcre2_jit=no ;; esac ]) ``` This is important to me because I'm planning on making --with-external-gd the default soon, and I myself am guilty of writing a test that disables certain formats when cross-compiling because they cannot be detected with AC_RUN_IFELSE. This bug report has given me second thoughts about doing that. ping @remicollet ### PHP Version git HEAD ### Operating System _No response_