Makefile: enable ASAN for GCC

Previously the `Makefile` conditionally enabled address sanitizer (ASAN)
based on whether the compiler was `clang`. Since GCC has supported
address sanitizer since GCC 4.8[0] we can remove this check and always
use ASAN for both supported compilers.

The only snag is that I observed linker errors about undefined
references to `__ubsan_handle_type_mismatch` unless I fix the `LDFLAGS`
to also include `-fsanitize=undefined`. This was already included in the
`CFLAGS`.

[0]: https://github.com/google/sanitizers/wiki/AddressSanitizer#getting-addresssanitizer

rustls-libssl/Makefile

@@ -5,10 +5,8 @@ CFLAGS := -Werror -Wall -Wextra -Wpedantic -g $(shell pkg-config --cflags openss
 PROFILE := debug
 
 ifeq ($(PROFILE), debug)
-ifeq ($(CC), clang)
 	CFLAGS += -fsanitize=address -fsanitize=undefined
-	LDFLAGS += -fsanitize=address
-endif
+	LDFLAGS += -fsanitize=address -fsanitize=undefined
 endif
 
 ifeq ($(PROFILE), release)