Don't suppress UBSan unless compiling with UBSan (cossacklabs#556)

Recently added SOTER_ED25519_NO_UBSAN macro is expanded into UBSan
tweaks even when we do not compile with Undefined Behavior sanitizer
enabled. This can produce ugly warnings on systems that do not support
all of the sanitizer flags.

Let's just expand this macro into a no-op if we are not compiling with
sanitizers. That's easier that deducing exactly which sanitizer flags
are supported to avoid compiler warnings.

Makefile

@@ -315,6 +315,7 @@ CFLAGS += -fvisibility=hidden
 #
 
 ifdef WITH_ASAN
+CFLAGS += -DWITH_ASAN
 ifeq (yes,$(call supported,-fsanitize=address))
 SANITIZERS += -fsanitize=address
 else
@@ -323,6 +324,7 @@ endif
 endif
 
 ifdef WITH_MSAN
+CFLAGS += -DWITH_MSAN
 ifeq (yes,$(call supported,-fsanitize=memory))
 SANITIZERS += -fsanitize=memory -fsanitize-memory-track-origins=2
 else
@@ -331,6 +333,7 @@ endif
 endif
 
 ifdef WITH_TSAN
+CFLAGS += -DWITH_TSAN
 ifeq (yes,$(call supported,-fsanitize=thread))
 SANITIZERS += -fsanitize=thread
 else
@@ -339,6 +342,7 @@ endif
 endif
 
 ifdef WITH_UBSAN
+CFLAGS += -DWITH_UBSAN
 ifeq (yes,$(call supported,-fsanitize=undefined))
 SANITIZERS += -fsanitize=undefined
 else

src/soter/ed25519/fe.h

@@ -13,14 +13,14 @@ typedef uint64_t crypto_uint64;
 
 typedef crypto_int32 fe[10];
 
-#if defined(__clang__)
+#if defined(WITH_UBSAN) && defined(__clang__)
 #define SOTER_ED25519_NO_UBSAN __attribute__((no_sanitize( \
     "shift", \
     "unsigned-integer-overflow", \
     "implicit-integer-sign-change", \
     "implicit-unsigned-integer-truncation", \
     "implicit-signed-integer-truncation")))
-#elif defined(__GNUC__)
+#elif defined(WITH_UBSAN) && defined(__GNUC__)
 #define SOTER_ED25519_NO_UBSAN __attribute__((no_sanitize("undefined")))
 #else
 #define SOTER_ED25519_NO_UBSAN