Get --ftrace working on aarch64

This change implements a new approach to function call logging, that's
based on the GCC flag: -fpatchable-function-entry. Read the commentary
in build/config.mk to learn how it works.

tool/viz/lib/doublechrominance.S

@@ -27,9 +27,10 @@
 //	@param	%rsi is char[edi/16][16] output and %rsi==%rdx is OK
 //	@param	%rdx is char[edi/16][8] input
 //	@return	%rax is %rsi
+	.ftrace1
 doublechrominance:
+	.ftrace2
 	.leafprologue
-	.profilable
 	shr	$1,%edi			# backwards algorithm
 	jbe	1f			# do nothing if !n || n%2
 	mov	%edi,%ecx

tool/viz/lib/vizlib.mk

@@ -50,7 +50,7 @@ TOOL_VIZ_LIB_A_DEPS :=					\
 	$(call uniq,$(foreach x,$(TOOL_VIZ_LIB_A_DIRECTDEPS),$($(x))))
 
 o/$(MODE)/tool/viz/lib/pmaddubsw.o: private		\
-		OVERRIDE_CFLAGS +=			\
+		CFLAGS +=				\
 			-fvect-cost-model=unlimited
 
 o/$(MODE)/tool/viz/lib/scale.o				\
@@ -69,12 +69,12 @@ o/$(MODE)/tool/viz/lib/getxtermcodes.o			\
 o/$(MODE)/tool/viz/lib/lingamma.o			\
 o/$(MODE)/tool/viz/lib/perlin3.o			\
 o/$(MODE)/tool/viz/lib/resizegraphic.o: private		\
-		OVERRIDE_CFLAGS +=			\
+		CFLAGS +=				\
 			-DSTACK_FRAME_UNLIMITED		\
 			$(MATHEMATICAL)
 
 o/$(MODE)/tool/viz/lib/printmatrix.o: private		\
-		OVERRIDE_CFLAGS +=			\
+		CFLAGS +=				\
 			$(IEEE_MATH)
 
 $(TOOL_VIZ_LIB_A):					\

tool/viz/viz.mk

@@ -98,12 +98,12 @@ o/$(MODE)/tool/viz/printvideo.com:			\
 	@$(MAKE_SYMTAB_ZIP)
 
 o/$(MODE)/tool/viz/derasterize.o: private	\
-		OVERRIDE_CFLAGS +=		\
+		CFLAGS +=			\
 			-DSTACK_FRAME_UNLIMITED	\
 			$(MATHEMATICAL)
 
 o/$(MODE)/tool/viz/magikarp.o: private		\
-		OVERRIDE_CFLAGS +=		\
+		CFLAGS +=			\
 			$(MATHEMATICAL)
 
 $(TOOL_VIZ_OBJS):				\