d: Remove the d_critsec_size target hook.

d: Remove the d_critsec_size target hook.

The allocation of mutex objects for synchronized statements has been
moved to the library as of merging druntime 58560d51.  All support code
in the compiler for getting the OS critical section size has been
removed along with it.

Reviewed-on: https://github.com/dlang/dmd/pull/11902
	     https://github.com/dlang/druntime/pull/3248

gcc/ChangeLog:

	* config/aarch64/aarch64-linux.h (GNU_USER_TARGET_D_CRITSEC_SIZE):
	Remove.
	* config/glibc-d.c (glibc_d_critsec_size): Likewise.
	(TARGET_D_CRITSEC_SIZE): Likewise.
	* config/i386/linux-common.h (GNU_USER_TARGET_D_CRITSEC_SIZE):
	Likewise.
	* config/sol2-d.c (solaris_d_critsec_size): Likewise.
	(TARGET_D_CRITSEC_SIZE):  Likewise.
	* doc/tm.texi.in (TARGET_D_CRITSEC_SIZE): Likewise.
	* doc/tm.texi: Regenerate.

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd bec5973b0.
	* d-target.cc (Target::critsecsize): Remove.
	* d-target.def: Remove d_critsec_size.

libphobos/ChangeLog:

	* libdruntime/MERGE: Merge upstream druntime 58560d51.