i386: Prefer PLT indirection for __fentry__ calls under -fPIC [PR119386]

i386: Prefer PLT indirection for __fentry__ calls under -fPIC [PR119386]

Commit bde21de1205 ("i386: Honour -mdirect-extern-access when calling
__fentry__") updated the logic that emits mcount() / __fentry__() calls
into function prologues when profiling is enabled, to avoid GOT-based
indirect calls when a direct call would suffice.

There are two problems with that change:
- it relies on -mdirect-extern-access rather than -fno-plt to decide
  whether or not a direct [PLT based] call is appropriate;
- for the PLT case, it falls through to x86_print_call_or_nop(), which
  does not emit the @PLT suffix, resulting in the wrong relocation to be
  used (R_X86_64_PC32 instead of R_X86_64_PLT32)

Fix this by testing flag_plt instead of ix86_direct_extern_access, and
updating x86_print_call_or_nop() to take flag_pic and flag_plt into
account. This also ensures that -mnop-mcount works as expected when
emitting the PLT based profiling calls.

While at it, fix the 32-bit logic as well, and issue a PLT call unless
PLTs are explicitly disabled.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119386

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
gcc/ChangeLog:

	PR target/119386
	* config/i386/i386.cc (x86_print_call_or_nop): Add @PLT suffix
	where appropriate.
	(x86_function_profiler): Fall through to x86_print_call_or_nop()
	for PIC codegen when flag_plt is set.

gcc/testsuite/ChangeLog:

	PR target/119386
	* gcc.target/i386/pr119386-1.c: New test.
	* gcc.target/i386/pr119386-2.c: New test.