Fix FLT_ROUNDS for WASI.

Author: sunfishcode

expected/wasm32-wasi/predefined-macros.txt

@@ -648,7 +648,7 @@
 #define FLT_MIN_10_EXP (-37)
 #define FLT_MIN_EXP (-125)
 #define FLT_RADIX 2
-#define FLT_ROUNDS (__flt_rounds())
+#define FLT_ROUNDS (__builtin_flt_rounds())
 #define FLT_TRUE_MIN 1.40129846432481707092e-45F
 #define FLUSHBAND 0x04
 #define FLUSHO 0010000

libc-top-half/musl/include/float.h

@@ -5,8 +5,12 @@
 extern "C" {
 #endif
 
+#ifdef __wasilibc_unmodified_upstream
 int __flt_rounds(void);
 #define FLT_ROUNDS (__flt_rounds())
+#else
+#define FLT_ROUNDS (__builtin_flt_rounds())
+#endif
 
 #define FLT_RADIX 2