Index: lib/builtins/int_types.h
===================================================================
--- lib/builtins/int_types.h
+++ lib/builtins/int_types.h
@@ -137,6 +137,18 @@
 #endif /* _YUGA_LITTLE_ENDIAN */
 } uqwords;
 
+/* Check if the target supports 80 bit extended precision long doubles.
+ * Notably, on x86 Windows, MSVC only provides a 64-bit long double, but GCC
+ * still makes it 80 bits. Clang will match whatever compiler it is trying to
+ * be compatible with.
+ */
+#if ((defined(__i386__) || defined(__x86_64__)) && !defined(_MSC_VER)) || \
+    defined(__m68k__) || defined(__ia64__)
+#define HAS_80_BIT_LONG_DOUBLE 1
+#else
+#define HAS_80_BIT_LONG_DOUBLE 0
+#endif
+
 typedef union
 {
     uqwords     u;
Index: test/builtins/Unit/fixxfdi_test.c
===================================================================
--- test/builtins/Unit/fixxfdi_test.c
+++ test/builtins/Unit/fixxfdi_test.c
@@ -26,7 +26,7 @@
 // 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)
 {