[libc][fenv] Add missing FE_* definitions for some environment. (llvm…

…#91519)

libc/hdr/fenv_macros.h

@@ -17,10 +17,51 @@
 
 #include <fenv.h>
 
+// In some environment, FE_ALL_EXCEPT is set to 0 and the remaining exceptions
+// FE_* are missing.
+#if (FE_ALL_EXCEPT == 0)
+#ifndef FE_DIVBYZERO
+#define FE_DIVBYZERO 0
+#endif // FE_DIVBYZERO
+
+#ifndef FE_INEXACT
+#define FE_INEXACT 0
+#endif // FE_INEXACT
+
+#ifndef FE_INVALID
+#define FE_INVALID 0
+#endif // FE_INVALID
+
+#ifndef FE_OVERFLOW
+#define FE_OVERFLOW 0
+#endif // FE_OVERFLOW
+
+#ifndef FE_UNDERFLOW
+#define FE_UNDERFLOW 0
+#endif // FE_UNDERFLOW
+#else
 // If this is not provided by the system, define it for use internally.
 #ifndef __FE_DENORM
 #define __FE_DENORM (1 << 6)
 #endif
+#endif
+
+// Rounding mode macros might be missing.
+#ifndef FE_DOWNWARD
+#define FE_DOWNWARD 0x400
+#endif // FE_DOWNWARD
+
+#ifndef FE_TONEAREST
+#define FE_TONEAREST 0
+#endif // FE_TONEAREST
+
+#ifndef FE_TOWARDZERO
+#define FE_TOWARDZERO 0xC00
+#endif // FE_TOWARDZERO
+
+#ifndef FE_UPWARD
+#define FE_UPWARD 0x800
+#endif // FE_UPWARD
 
 #endif // LLVM_LIBC_FULL_BUILD