Index: compiler-rt/lib/builtins/emutls.c
===================================================================
--- compiler-rt/lib/builtins/emutls.c
+++ compiler-rt/lib/builtins/emutls.c
@@ -26,12 +26,23 @@
 #define EMUTLS_SKIP_DESTRUCTOR_ROUNDS 0
 #endif
 
+#ifdef _MSC_VER && !defined(__clang__)
+// MSVC raises a warning about a nonstandard extension being used for the 0
+// sized element in this array. Disable this for warn-as-error builds.
+#pragma warning(push)
+#pragma warning(disable : 4206)
+#endif
+
 typedef struct emutls_address_array {
   uintptr_t skip_destructor_rounds;
   uintptr_t size; // number of elements in the 'data' array
   void *data[];
 } emutls_address_array;
 
+#ifdef _MSC_VER && !defined(__clang__)
+#pragma warning(pop)
+#endif
+
 static void emutls_shutdown(emutls_address_array *array);
 
 #ifndef _WIN32
Index: compiler-rt/lib/builtins/fixunsxfdi.c
===================================================================
--- compiler-rt/lib/builtins/fixunsxfdi.c
+++ compiler-rt/lib/builtins/fixunsxfdi.c
@@ -25,6 +25,13 @@
 // eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
 // mmmm mmmm mmmm
 
+#ifdef _MSC_VER
+// MSVC throws a warning about 'unitialized variable use' here,
+// disable it for builds that warn-as-error
+#pragma warning(push)
+#pragma warning(disable : 4700)
+#endif
+
 COMPILER_RT_ABI du_int __fixunsxfdi(long double a) {
   long_double_bits fb;
   fb.f = a;
@@ -36,4 +43,6 @@
   return fb.u.low.all >> (63 - e);
 }
 
+#ifdef _MSC_VER
+#pragma warning(pop)
 #endif
Index: compiler-rt/lib/builtins/fixunsxfsi.c
===================================================================
--- compiler-rt/lib/builtins/fixunsxfsi.c
+++ compiler-rt/lib/builtins/fixunsxfsi.c
@@ -25,6 +25,13 @@
 // eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
 // mmmm mmmm mmmm
 
+#ifdef _MSC_VER
+// MSVC throws a warning about 'unitialized variable use' here,
+// disable it for builds that warn-as-error
+#pragma warning(push)
+#pragma warning(disable : 4700)
+#endif
+
 COMPILER_RT_ABI su_int __fixunsxfsi(long double a) {
   long_double_bits fb;
   fb.f = a;
@@ -36,4 +43,8 @@
   return fb.u.low.s.high >> (31 - e);
 }
 
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
+
 #endif // !_ARCH_PPC
Index: compiler-rt/lib/builtins/fixxfdi.c
===================================================================
--- compiler-rt/lib/builtins/fixxfdi.c
+++ compiler-rt/lib/builtins/fixxfdi.c
@@ -24,6 +24,13 @@
 // eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
 // mmmm mmmm mmmm
 
+#ifdef _MSC_VER
+// MSVC throws a warning about 'unitialized variable use' here,
+// disable it for builds that warn-as-error
+#pragma warning(push)
+#pragma warning(disable : 4700)
+#endif
+
 COMPILER_RT_ABI di_int __fixxfdi(long double a) {
   const di_int di_max = (di_int)((~(du_int)0) / 2);
   const di_int di_min = -di_max - 1;
@@ -41,3 +48,7 @@
 }
 
 #endif // !_ARCH_PPC
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
\ No newline at end of file
Index: compiler-rt/lib/builtins/udivmoddi4.c
===================================================================
--- compiler-rt/lib/builtins/udivmoddi4.c
+++ compiler-rt/lib/builtins/udivmoddi4.c
@@ -17,6 +17,13 @@
 
 // Translated from Figure 3-40 of The PowerPC Compiler Writer's Guide
 
+#ifdef _MSC_VER
+// MSVC throws a warning about mod 0 here, disable it for builds that
+// warn-as-error
+#pragma warning(push)
+#pragma warning(disable : 4724)
+#endif
+
 COMPILER_RT_ABI du_int __udivmoddi4(du_int a, du_int b, du_int *rem) {
   const unsigned n_uword_bits = sizeof(su_int) * CHAR_BIT;
   const unsigned n_udword_bits = sizeof(du_int) * CHAR_BIT;
@@ -187,3 +194,7 @@
     *rem = r.all;
   return q.all;
 }
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
\ No newline at end of file