Configure problem when cross-compiling PostgreSQL 16.1

Hi all,

I was trying to cross-compile PostgreSQL 16.1 using Buildroot which worked fine
until I executed "initdb" on my target device, where I faced the following error:

2023-12-06 07:10:18.568 UTC [31] FATAL: could not load library
"/usr/lib/postgresql/dict_snowball.so": /usr/lib/postgresql/dict_snowball.so:
undefined symbol: CurrentMemoryContext

It turned out that the "postgres" binary was missing the symbol
"CurrentMemoryContext" because the configure script assumed that my toolchain's
(GCC 9.4) linker does not support "--export-dynamic", although it supports it.

I had a quick look at the configure script where the following lines peeked my
interest:

if test "$cross_compiling" = yes; then :
pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl___export_dynamic="assuming no"

Apparently when cross-compiling the linker is automatically assumed to not
understand "--export-dynamic", leading to aforementioned problem on my end.

A workaround of mine is to override
pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl___export_dynamic with "yes", which makes
everything work as expected.

There is also at least one additional linker flag "--as-needed" that is not
being used when cross-compiling. Is this a bug or am I misunderstanding the
implications that PostgreSQL has when "$cross_compiling=yes"?

Best regards,
Dominik