Bug 1271959 - Don't specify a size for enum class SimdType. r=bbouvier

There is a bug in GCC 4.8 that miscompiles some uses of an enum with uint8_t
size. Work around this compiler bug by not specifying a size for SimdType.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64037

js/src/builtin/SIMD.h

@@ -755,7 +755,7 @@ namespace js {
 // It must be kept in sync with the enumeration of values in
 // TypedObjectConstants.h; in particular we need to ensure that Count is
 // appropriately set with respect to the number of actual types.
-enum class SimdType : uint8_t {
+enum class SimdType {
     Int8x16   = JS_SIMDTYPEREPR_INT8X16,
     Int16x8   = JS_SIMDTYPEREPR_INT16X8,
     Int32x4   = JS_SIMDTYPEREPR_INT32X4,

js/src/builtin/TypedObject.h

@@ -327,7 +327,7 @@ class ComplexTypeDescr : public TypeDescr
     }
 };
 
-enum class SimdType : uint8_t;
+enum class SimdType;
 
 /*
  * SIMD Type descriptors.

js/src/jit/Recover.cpp

@@ -1335,7 +1335,7 @@ MSimdBox::writeRecoverData(CompactBufferWriter& writer) const
 {
     MOZ_ASSERT(canRecoverOnBailout());
     writer.writeUnsigned(uint32_t(RInstruction::Recover_SimdBox));
-    static_assert(sizeof(SimdType) == sizeof(uint8_t), "assuming uint8 storage class for SimdType");
+    static_assert(unsigned(SimdType::Count) < 0x100, "assuming SimdType fits in 8 bits");
     writer.writeByte(uint8_t(simdType()));
     return true;
 }

js/src/vm/GlobalObject.h

@@ -31,7 +31,7 @@ class StaticBlockScope;
 class ClonedBlockObject;
 
 class SimdTypeDescr;
-enum class SimdType : uint8_t;
+enum class SimdType;
 
 /*
  * Global object slots are reserved as follows: