gdb/testsuite: don't avoid DWARF assembler tests with Clang

gdb/testsuite: don't avoid DWARF assembler tests with Clang

Two tests make the claim that the DWARF assembler requires gcc,
however, this isn't true.  I think at one point, when the DWARF
assembler was first added, we did use some techniques that were not
portable (see the comments in lib/dwarf.exp on function_range for
details), however, I think most DWARF assembler tests will now work
fine with Clang.

The two tests that I modify in this commit both work fine with Clang,
at least, I've tested with Clang 9.0.1 and 15.0.2, and don't see any
problems, so I'm removing the early return logic that stops these
tests from running with Clang.

Reviewed-By: Lancelot SIX <lancelot.six@amd.com>