libgcc, aarch64, Darwin: Initial libgcc boiler-plate changes.

Initial changes to build libgcc for aarch64 Darwin (declare the port,
handle Mach-O assembler syntax and arrange for building the main extra
pieces).

libgcc/config.host

@@ -82,7 +82,7 @@ m32c*-*-*)
         cpu_type=m32c
 	tmake_file=t-fdpbit
         ;;
-aarch64*-*-*)
+aarch64*-*-* | arm64*-*-*)
 	cpu_type=aarch64
 	;;
 alpha*-*-*)
@@ -407,6 +407,14 @@ aarch64*-*-elf | aarch64*-*-rtems*)
 	tmake_file="${tmake_file} ${cpu_type}/t-softfp t-softfp t-crtfm"
 	md_unwind_header=aarch64/aarch64-unwind.h
 	;;
+aarch64*-*darwin* | arm64*-*darwin* )
+	extra_parts="$extra_parts crtfastmath.o"
+	tmake_file="${tmake_file} ${cpu_type}/t-aarch64"
+	tmake_file="${tmake_file} ${cpu_type}/t-lse "
+	tmake_file="${tmake_file} t-crtfm"
+	# No soft float for now because our long double is DF not TF.
+	md_unwind_header=aarch64/aarch64-unwind.h
+	;;
 aarch64*-*-freebsd*)
 	extra_parts="$extra_parts crtfastmath.o"
 	tmake_file="${tmake_file} ${cpu_type}/t-aarch64"

libgcc/config/aarch64/lse.S

@@ -58,7 +58,11 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #endif
 
 /* Declare the symbol gating the LSE implementations.  */
+#if __ELF__
 	.hidden	__aarch64_have_lse_atomics
+#else
+	.private_extern	__aarch64_have_lse_atomics
+#endif
 
 /* Turn size and memory model defines into mnemonic fragments.  */
 #if SIZE == 1
@@ -139,6 +143,7 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define BTI_C	hint	34
 
 /* Start and end a function.  */
+#if __ELF__
 .macro	STARTFN name
 	.text
 	.balign	16
@@ -162,6 +167,29 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 	cbz	w(tmp0), \label
 .endm
 
+#else
+.macro	STARTFN name
+	.text
+	.balign	16
+	.private_extern	_\name
+	.cfi_startproc
+_\name:
+	BTI_C
+.endm
+
+.macro	ENDFN name
+	.cfi_endproc
+.endm
+
+/* Branch to LABEL if LSE is disabled.  */
+.macro	JUMP_IF_NOT_LSE label
+	adrp	x(tmp0), ___aarch64_have_lse_atomics@PAGE
+	ldrb	w(tmp0), [x(tmp0), ___aarch64_have_lse_atomics@PAGEOFF]
+	cbz	w(tmp0), \label
+.endm
+
+#endif
+
 #ifdef L_cas
 
 STARTFN	NAME(cas)

libgcc/config/aarch64/t-darwin

@@ -0,0 +1,7 @@
+# FIXME: decide what we need here, or delete this file.
+
+HOST_LIBGCC2_CFLAGS += -mmacosx-version-min=11.0
+
+LIB2_SIDITI_CONV_FUNCS = yes
+
+BUILD_LIBGCCS1 =