Implement the extension GL_ARB_gpu_shader_int64

- Add new keyword int64_t/uint64_t/i64vec/u64vec.
- Support 64-bit integer literals (dec/hex/oct).
- Support built-in operators for 64-bit integer type.
- Add implicit and explicit type conversion for 64-bit integer type.
- Add new built-in functions defined in this extension.

glslang/MachineIndependent/linkValidate.cpp

@@ -880,6 +880,8 @@ const int baseAlignmentVec4Std140 = 16;
 int TIntermediate::getBaseAlignmentScalar(const TType& type, int& size)
 {
     switch (type.getBasicType()) {
+    case EbtInt64:
+    case EbtUint64:
     case EbtDouble:  size = 8; return 8;
     default:         size = 4; return 4;
     }