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.

third_party/mbedtls/mbedtls.mk

@@ -48,27 +48,27 @@ $(THIRD_PARTY_MBEDTLS_A).pkg:						\
 		$(foreach x,$(THIRD_PARTY_MBEDTLS_A_DIRECTDEPS),$($(x)_A).pkg)
 
 $(THIRD_PARTY_MBEDTLS_A_OBJS): private					\
-			OVERRIDE_CFLAGS +=				\
+			CFLAGS +=					\
 				-fdata-sections				\
 				-ffunction-sections
 
 o/$(MODE)/third_party/mbedtls/everest.o: private			\
-			OVERRIDE_CFLAGS +=				\
+			CFLAGS +=					\
 				-O3
 
 o/$(MODE)/third_party/mbedtls/bigmul4.o					\
 o/$(MODE)/third_party/mbedtls/bigmul6.o: private			\
-			OVERRIDE_CFLAGS +=				\
+			CFLAGS +=					\
 				-O2
 
 ifeq ($(ARCH), x86_64)
 o/$(MODE)/third_party/mbedtls/shiftright-avx.o: private			\
-			OVERRIDE_CFLAGS +=				\
+			CFLAGS +=					\
 				-O3 -mavx
 endif
 
 o/$(MODE)/third_party/mbedtls/zeroize.o: private			\
-			OVERRIDE_CFLAGS +=				\
+			CFLAGS +=					\
 				-O3					\
 				-x-no-pg				\
 				-fomit-frame-pointer			\

third_party/mbedtls/test/test.mk

@@ -135,7 +135,7 @@ o/$(MODE)/third_party/mbedtls/test/%.com.runs: o/$(MODE)/third_party/mbedtls/tes
 	@$(COMPILE) -ACHECK -wtT$@ $(VM) $< $(TESTARGS)
 
 o/$(MODE)/third_party/mbedtls/test/lib.o: private								\
-			OVERRIDE_CFLAGS +=									\
+			CFLAGS +=										\
 				-fdata-sections									\
 				-ffunction-sections
 

third_party/mbedtls/test/test_suite_ssl.c

@@ -91,7 +91,7 @@ void log_analyzer( void *ctx, int level,
 
 /* Invalid minor version used when not specifying a min/max version or expecting a test to fail */
 #define TEST_SSL_MINOR_VERSION_NONE -1
-s
+
 typedef struct handshake_test_options
 {
     const char *cipher;