libgomp testsuite: Don't amend 'LD_LIBRARY_PATH' for system-provided HSA Runtime...

libgomp testsuite: Don't amend 'LD_LIBRARY_PATH' for system-provided HSA Runtime library

This is only active if GCC is 'configure'd with '--with-hsa-runtime=[...]' or
'--with-hsa-runtime-lib=[...]' -- which nobody really is doing, as far as I can
tell.

'libgomp/testsuite/lib/libgomp.exp:libgomp_init' states:

    # For build-tree testing, also consider the library paths used for builing.
    # For installed testing, we assume all that to be provided in the sysroot.
    if { $blddir != "" } {
        [...]
        global hsa_runtime_lib
        if { $hsa_runtime_lib != "" } {
            append always_ld_library_path ":$hsa_runtime_lib"
        }
    }

However, the libgomp GCN plugin is unconditionally built against the
GCC-shipped 'include/hsa*.h' header files, and at run time does
'dlopen("libhsa-runtime64.so.1")', so there is no system-provided HSA Runtime
library "used for builing".  It thus doesn't make sense to amend
'LD_LIBRARY_PATH' for system-provided HSA Runtime library.

	libgomp/
	* testsuite/lib/libgomp.exp (libgomp_init): Don't
	'append always_ld_library_path ":$hsa_runtime_lib"'.
	* testsuite/libgomp-test-support.exp.in (hsa_runtime_lib): Don't set.

(cherry picked from commit 2e309a4eff80e55b53d32d26926a2a94eabfea21)