Scanner/PP: Fix the infinite loop when an input file lacks EOF

The input scanner can be trapped in an infinite loop if the given input
file does not have EOF (and is not ended with a 'whitespace').

The problem is caused by unget(), which keeps rolling back the scanner
pointer without hitting an EOF at the end of the file. This makes getch()
function keep returning the last character of the file and never ends,
and the effect of advance() is always counteracted by unget().

SPV: Use OpLogicalEqual/OpLogicalNotEqual for boolean type comparison.

Remove use of std::mutex in gtest code.

Gtest runs in single-threaded mode.  So the GlslangInitializer
object in the test code doesn't have to do its own synchronization.

SPV: Spec-consts: Fix constructors matrix and vector

fix the problem that spec constant composite instruction being used when only front-end constants are used in the constructor

Fix issue: #237

1. The code generated for matrix constructor should 1) build column
vectors first, 2) build matrix with the vectors.

2. When there is only one scalar type constituent in vector's
constructor, we should populate the constituent to fill all the slots in
the vector. As for matrix, the single constituent should be populated to
the diagonal positions (top-left to bottom-right diagonal).

remove createSpvConstantFromConstSubTree()

SPV: SpecOp bool->uint/int and uint<->int conversion

Bool -> uint/int with OpSpecConstantOp OpSelect instruction.

uint <-> int conversion with OpSpecConstantOp OpIAdd instruction.

Note, implicit conversion: `const uint = an_int_spec_constant` is not
supported. Explicit type casting is required: `const uint =
uint(an_int_spec_constant)`

Unit test executable should link to libHLSL

No unit tests exercise it.

A couple of small warning fixes

This might address issue #221, which I couldn't reproduce.

This is according to the expected KHR_vulkan_glsl without floating point.
So, floating-point spec-const operations no longer work, and that's
reflected in the tests.

SPV: Generate OpSpecConstantOp for all subtrees indicated by the AST.

Move SpecConstantOpModeGuard from makeSpvConstantFromConstSubTree() to
visitbinary() and visitunary(). Checking if the visiting node is a spec
constants, if so, turn on the SpecConstantOpMode, otherwise, stay in the
normal mode.

fix the wrong generated code when a non-constant array is declared with its size derived from spec constant operations

Handle built-in constants redeclared with a specialization constant id.

Support declaring built-in values as spec constants.

Refine the code in createSpvConstant().

VS2010 compile fixes

Fix spelling mistakes

Add Google Test as the new test framework

Parser: Update array size of gl_ClipDistance/gl_CullDistance in gl_in[].

SPV: Spec Constant Operations

fix format; remove unnecessary parameters; rename some spec op mode guard class; remove support of float point comparison and composite type comparison; update the tests.