libstdc++: Use GCC_TRY_COMPILE_OR_LINK for getentropy, arc4random

Since r12-5056-g3439657b0286, there has been a regression in
test results; an additional 100 FAILs running the g++ and
libstdc++ testsuite on cris-elf, a newlib target.  The
failures are linker errors, not finding a definition for
getentropy.  It appears newlib has since 2017-12-03
declarations of getentropy and arc4random, and provides an
implementation of arc4random using getentropy, but provides no
definition of getentropy, not even a stub yielding ENOSYS.
This is similar to what it does for many other functions too.

While fixing newlib (like adding said stub) would likely help,
it still leaves older newlib releases hanging.  Thankfully,
the libstdc++ configury test can be improved to try linking
where possible; using the bespoke GCC_TRY_COMPILE_OR_LINK
instead of AC_TRY_COMPILE.  BTW, I see a lack of consistency;
some tests use AC_TRY_COMPILE and some GCC_TRY_COMPILE_OR_LINK
for no apparent reason, but this commit just amends
r12-5056-g3439657b0286.

libstdc++-v3:
	PR libstdc++/103166
	* acinclude.m4 (GLIBCXX_CHECK_GETENTROPY, GLIBCXX_CHECK_ARC4RANDOM):
	Use GCC_TRY_COMPILE_OR_LINK instead of AC_TRY_COMPILE.
	* configure: Regenerate.