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.

test/libc/intrin/test.mk

@@ -69,7 +69,7 @@ o/$(MODE)/test/libc/intrin/lock_test.com.dbg:		\
 	@$(APELINK)
 
 $(TEST_LIBC_INTRIN_OBJS): private			\
-		OVERRIDE_CFLAGS +=			\
+		CFLAGS +=				\
 			-fno-builtin
 
 .PHONY: o/$(MODE)/test/libc/intrin

test/libc/runtime/test.mk

@@ -77,7 +77,7 @@ o/$(MODE)/test/libc/runtime/getenv_test.com.runs:		\
 	@HELLO=THERE build/runit $@ $<
 
 o/$(MODE)/test/libc/runtime/itsatrap_test.o: private		\
-		OVERRIDE_CFLAGS +=				\
+		CFLAGS +=					\
 			-fno-sanitize=all			\
 			-ftrapv
 

test/libc/str/test.mk

@@ -63,7 +63,7 @@ o/$(MODE)/test/libc/str/str.pkg:					\
 		$(foreach x,$(TEST_LIBC_STR_DIRECTDEPS),$($(x)_A).pkg)
 
 o/$(MODE)/test/libc/str/tpenc_test.o: private				\
-		OVERRIDE_CFLAGS +=					\
+		CFLAGS +=						\
 			$(TRADITIONAL)
 
 o/$(MODE)/test/libc/str/%.com.dbg:					\
@@ -80,7 +80,7 @@ $(TEST_LIBC_STR_OBJS): private						\
 			-fno-builtin
 
 o/$(MODE)/test/libc/str/memmove_test.o: private				\
-		OVERRIDE_CFLAGS +=					\
+		CFLAGS +=						\
 			-O2 -D_FORTIFY_SOURCE=2
 
 .PHONY: o/$(MODE)/test/libc/str

test/libc/thread/test.mk

@@ -56,7 +56,7 @@ o/$(MODE)/test/libc/thread/%.com.dbg:			\
 	@$(APELINK)
 
 o/$(MODE)/test/libc/thread/pthread_create_test.o:	\
-		private OVERRIDE_CPPFLAGS +=		\
+		private CPPFLAGS +=			\
 			-DSTACK_FRAME_UNLIMITED
 
 .PHONY: o/$(MODE)/test/libc/thread

test/libc/tinymath/test.mk

@@ -58,7 +58,7 @@ o/$(MODE)/test/libc/tinymath/%.com.dbg:				\
 	@$(APELINK)
 
 $(TEST_LIBC_TINYMATH_OBJS): private				\
-		OVERRIDE_CFLAGS +=				\
+		CFLAGS +=					\
 			-fno-builtin
 
 .PHONY: o/$(MODE)/test/libc/tinymath