Revert "Revert "New testcase for KFAIL of "FIXME in gcc_convert_symbol".""

This reverts commit c500d0b1c575730eb2cb5ac0d8396a9bc139c152.

Conflicts:
	gdb/testsuite/gdb.base/compile.c
	gdb/testsuite/gdb.base/compile.exp
fix "extern" problems

this fixes "extern" nesting problems
it introduces a new scope for the user's code so that
we can put gdb-provided decls into the function scope
without clashes
and, it fixes a FIXME regarding whether variables from the static
scope should be treated as extern (they shouldn't)