Revert 1689ad2 "[builtins] Implement rounding mode support for i386/x86_64"

It broke the build with MSVC:

fp_mode.c(20): error C2065: '__asm__': undeclared identifier

> Differential Revision: https://reviews.llvm.org/D69870

Author: zmodem

compiler-rt/lib/builtins/CMakeLists.txt

@@ -239,7 +239,6 @@ set(x86_ARCH_SOURCES
   floatuntixf.c
   mulxc3.c
   powixf2.c
-  i386/fp_mode.c
 )
 
 if (NOT MSVC)

compiler-rt/lib/builtins/i386/fp_mode.c

@@ -76,8 +76,7 @@ int main()
                      UINT64_C(0x61e58dd6c51eb77c)))
         return 1;
 
-#if (defined(__arm__) || defined(__aarch64__)) && defined(__ARM_FP) || \
-    defined(i386) || defined(__x86_64__)
+#if (defined(__arm__) || defined(__aarch64__)) && defined(__ARM_FP)
     // Rounding mode tests on supported architectures
     const long double m = 1234.0L, n = 0.01L;
 

compiler-rt/test/builtins/Unit/addtf3_test.c

@@ -69,8 +69,7 @@ int main()
                      UINT64_C(0xa44a7bca780a166c)))
         return 1;
 
-#if (defined(__arm__) || defined(__aarch64__)) && defined(__ARM_FP) || \
-    defined(i386) || defined(__x86_64__)
+#if (defined(__arm__) || defined(__aarch64__)) && defined(__ARM_FP)
     // Rounding mode tests on supported architectures
     const long double m = 1234.02L, n = 0.01L;