Introduce -fprofile-update=prefer-atomic

Introduce -fprofile-update=prefer-atomic

	PR bootstrap/78069
	* common.opt: Add prefer-atomic as a new enum value for
	-fprofile-update.
	* coretypes.h: Likewise.
	* doc/invoke.texi: Document the new option value.
	* gcc.c: Replace atomic with prefer-atomic.  Remove warning.
	* tree-profile.c (tree_profiling): Select default value
	of -fprofile-update when 'prefer-atomic' is selected.
	PR bootstrap/78069
	* gcc.dg/no_profile_instrument_function-attr-1.c: Update test
	to match scanned pattern.
	* gcc.dg/tree-ssa/ssa-lim-11.c: Likewise.

From-SVN: r242386