Fix 30808 gprofng tests failed

Fix 30808 gprofng tests failed

In gprofng testing, we need a tempory gprofng installation to resolve run-time
dependencies on libraries (libgprofng, libopcodes, libbfd, etc).
We set LD_LIBRARY_PATH and GPROFNG_SYSCONFDIR to find our libraries and
configuration file. These variables must be set for all gprofng tests.

Tested on aarch64 and x86_64 with and without --enable-shared and --target=<>.

gprofng/ChangeLog
2023-08-31  Vladimir Mezentsev  <vladimir.mezentsev@oracle.com>

	PR gprofng/30808
	* testsuite/config/default.exp: Make a temporary install dir.
	Set LD_LIBRARY_PATH, GPROFNG_SYSCONFDIR.
	* testsuite/lib/Makefile.skel: Move LD_LIBRARY_PATH and
	GPROFNG_SYSCONFDIR setting in testsuite/config/default.exp.