options.exp: unsupport tests that depend on missing language

options.exp: unsupport tests that depend on missing language

There's a help.exp test that checks that the help message for
-Wabsolute-value mentions it's available in C and ObjC, when compiling
a C++ program.

However, if GCC is built with the C++ language disabled, the
.cc file is compiled as C, and the message [available in C...] becomes
[disabled] instead, because that's the default for the flag in C.

I suppose it might also be possible to disable the C language, and
then the multitude of help.exp tests that name c as the source
language will fail.

This patch avoids these fails: it detects the message "compiler not
installed" in the compiler output, and bails out as "unsupported".

for  gcc/testsuite/ChangeLog

	* lib/options.exp (check_for_options_with_filter): Detect
	unavailable compiler for the selected language, and bail out
	as unsupported.