sanitizer: Fix endianness checks for gcc

[• koriakin]

Summary

BIG_ENDIAN and LITTLE_ENDIAN are not supported by gcc, which
eg. for ubsan Value::getFloatValue will silently fall through to
the little endian branch, breaking display of float values by ubsan.
Use BYTE_ORDER == ORDER_BIG/LITTLE_ENDIAN as the condition
instead, which is supported by both clang and gcc.

Noticed while porting ubsan to s390x.

[• koriakin]

Ping?

[samsonov]

We use __BIG_ENDIAN__ and __LITTLE_ENDIAN__ macro in a few places in sanitizers. Let's update all these use cases to a more portable form for consistency.

[• koriakin]

Added a few other places in sanitizers. There are a few uses left, but these are in areas that shouldn't be hit by gcc/clang.

[samsonov]

LGTM. Thank you for fixing this!

[• koriakin]

I don't have svn write access, how can I get this patch commited?

lib/ubsan/ubsan_value.cc

 #endif
       case 32: {
         float Value;
-#if defined(__BIG_ENDIAN__)
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
        // For big endian the float value is in the last 4 bytes.
        // On some targets we may only have 4 bytes so we count backwards from
        // the end of Val to account for both the 32-bit and 64-bit cases.