diff -up chromium-61.0.3163.79/base/numerics/safe_math_clang_gcc_impl.h.fixgccagain chromium-61.0.3163.79/base/numerics/safe_math_clang_gcc_impl.h
--- chromium-61.0.3163.79/base/numerics/safe_math_clang_gcc_impl.h.fixgccagain	2017-09-06 15:48:27.560803028 -0400
+++ base/numerics/safe_math_clang_gcc_impl.h	2017-09-06 15:50:08.715853695 -0400
@@ -126,6 +126,7 @@ struct ClampedAddFastOp {
   }
 };
 
+#if defined(__clang__)  // Not supported on GCC.
 // This is the fastest negation on Intel, and a decent fallback on arm.
 __attribute__((always_inline)) inline int8_t ClampedNegate(uint8_t value) {
   uint8_t carry;
@@ -169,6 +170,7 @@ __attribute__((always_inline)) inline in
 __attribute__((always_inline)) inline int64_t ClampedNegate(int64_t value) {
   return ClampedNegate(static_cast<uint64_t>(value));
 }
+#endif
 
 template <typename T, typename U>
 struct ClampedSubFastOp {
@@ -180,6 +182,7 @@ struct ClampedSubFastOp {
       return ClampedSubFastAsmOp<T, U>::template Do<V>(x, y);
     }
 
+#if defined(__clang__)  // Not supported on GCC.
     // Fast path for generic clamped negation.
     if (std::is_same<T, U>::value && std::is_same<U, V>::value &&
         IsCompileTimeConstant(x) && x == 0 && !IsCompileTimeConstant(y)) {
@@ -190,6 +193,7 @@ struct ClampedSubFastOp {
               IntegerBitsPlusSign<T>::value, std::is_signed<T>::value>::type>(
               y));
     }
+#endif
 
     V result;
     return !__builtin_sub_overflow(x, y, &result)
diff -up chromium-61.0.3163.79/base/numerics/safe_math_shared_impl.h.fixgcc3 chromium-61.0.3163.79/base/numerics/safe_math_shared_impl.h
--- base/numerics/safe_math_shared_impl.h.fixgcc3	2017-09-06 16:30:15.898454585 -0400
+++ base/numerics/safe_math_shared_impl.h	2017-09-06 16:30:27.570229539 -0400
@@ -21,8 +21,7 @@
 #if !defined(__native_client__) &&                         \
     ((defined(__clang__) &&                                \
       ((__clang_major__ > 3) ||                            \
-       (__clang_major__ == 3 && __clang_minor__ >= 4))) || \
-     (defined(__GNUC__) && __GNUC__ >= 5))
+       (__clang_major__ == 3 && __clang_minor__ >= 4))))
 #include "base/numerics/safe_math_clang_gcc_impl.h"
 #define BASE_HAS_OPTIMIZED_SAFE_MATH (1)
 #else