[builtins] Re-enable x86-only long double tests

[rnk]

Summary

In r81552, the HAS_80_BIT_LONG_DOUBLE macro was added to the unit test
only version of int_lib.h. One month later in r85260 the duplicate
int_lib.h was removed, but the tests still passed because we don't build
with -Werror.

This is the minimal change to bring it back, and I decided to put the
configuration macro next to our 128-bit integer support macro.

[joerg]

__m68k__ and __ia64__ too, just for completeness.

[mstorsjo]

LGTM, modulo Joerg's comment.

compiler-rt/lib/builtins/int_types.h

#if _YUGA_LITTLE_ENDIAN
     udwords low;
     udwords high;
 #else
     udwords high;
     udwords low;
 #endif /* _YUGA_LITTLE_ENDIAN */
 } uqwords;
 
+/* Indicate if we have an Intel style extended 80 bit long double. Notably, on
+ * Windows, MSVC makes long double 64 bits, but GCC still makes it 80 bits.
+ * Clang will match whatever compiler it is pretending to be.
+ */
+#if (defined(__i386__) || defined(__x86_64__)) && !defined(_MSC_VER)
+#define HAS_80_BIT_LONG_DOUBLE 1
+#else
+#define HAS_80_BIT_LONG_DOUBLE 0
+#endif
+
 typedef union
 {
     uqwords     u;
     long double f;
 } long_double_bits;
 
 #if __STDC_VERSION__ >= 199901L
 typedef float _Complex Fcomplex;

compiler-rt/test/builtins/Unit/fixxfdi_test.c

 
 // Assumption: long double is an intel 80 bit floating point type padded with 6 bytes
 //             su_int is a 32 bit integral type
 //             value in long double is representable in di_int (no range checking performed)
 
 // gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
 // 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
 
-COMPILER_RT_ABI di_int __sfixxfdi(long double a);
+COMPILER_RT_ABI di_int __fixxfdi(long double a);
 
 int test__fixxfdi(long double a, di_int expected)
 {
     di_int x = __fixxfdi(a);
     if (x != expected)
         printf("error in __fixxfdi(%LA) = %llX, expected %llX\n",
                a, x, expected);
     return x != expected;