backtracing in a called function.
* gdb.base/constvars.exp: Only set lang to C++ if we're
compiling the test with HP's compilers.
* gdb.base/volatile.exp: Similarly.
* lib/gdb.exp (test_debug_format): New proc.
(setup_xfail_format): Use new proc test_debug_format.
* gdb.base/constvars.exp (local_compiler_xfail_check): New
proc; use new service proc test_debug_format.
Replace all other "gcc_compiled" tests with this test.
* gdb.base/volatile.exp (local_compiler_xfail_check): New
proc; use new service proc test_debug_format.
Replace all other "gcc_compiled" tests with this test.