Allow changing the fentry section per file and per function

Allow changing the fentry section per file and per function

When dynamically patching in/out instrumentation it can be useful
to handle different classes of functions differently. Add support
for changing the fentry section name on the command line
or as a function attributes. This allows to mark functions differently,
and handle them differently in dynamic patching.

gcc/:

2018-11-29  Andi Kleen  <ak@linux.intel.com>

	* config/i386/i386.c (current_fentry_section): Add.
	(x86_function_profiler): Handle fentry section.
	(ix86_attribute_table): Add fentry section.
	* config/i386/i386.opt: Add -mfentry-section.
	* doc/extend.texi: Document fentry_section attribute.
	* doc/invoke.texi: Document -mfentry-section.

gcc/testsuite/:

2018-11-29  Andi Kleen  <ak@linux.intel.com>

	* gcc.target/i386/fentryname2.c: New test.
	* gcc.target/i386/fentryname3.c: New test.

From-SVN: r266654