SPIR-V: Add support for texelFetch

SPIRV: Decorate matrices and arrays with their strides

cmake: Don't override CMAKE_INSTALL_PREFIX

Preprocessor:  'defined' cannot be used as a macro name in #define or #undef.

There's nothing really special about texelFetch other than the opcode and
some restrictions so adding it is pretty trivial.

Stop forcing CMAKE_INSTALL_PREFIX="install". If the user manually set
CMAKE_INSTALL_PREFIX, then trust that he knows what he's doing.

This patch does NOT change the project's default value ("install") of
CMAKE_INSTALL_PREFIX.

Change-Id: I81b46dd1986427b498fe6316bed03f01689987d4

"No layout(location=) is required if there is only one output" should not count
built-in variables like gl_SampleMask.  This is fixed.

Backward incompatible: Turn on PureOperatorBuiltins: use only enum-based built-in functions in the AST.

If this breaks your AST consumer, best is to modify it to test
against the enum values instead of doing string comparisons on
built-in function names.  This is the reason the change was made.

If you need the old behavior, you should be able to get it back by changing
PureOperatorBuiltins to be false instead of true.  This path will work for
a while, but is marked deprecated.

Also, the old behavior is tagged as release 2.4.

This is to avoid all need to do text comparison of built-in function names
when consuming the AST.  All built-in functions get enumerants.

Will want to turn on soon.  See PureOperatorBuiltins.  See issue #8.

Add more TOperator: fma/frexp/ldexp, AddCarry/SubBorrow/MulExtended/Bit*/Find*, (un)pack4x8/2x32, ftransform.

Also corrects some existing ones missing the "Op" part of their name.

Fixes for compiling glslang on Android.

Primarily fix is due to Android not supporting std::to_string().

Fix two multi-sample bugs: 1) include MS in name mangling, 2) add 'sample' argument texelFetch(*MS*,...).

Fixed VS2015 build

SPIR-V: Return undefined values from implicit returns instead of dummy

Add missing OpTypeSampledImage to prevent unknown type error from SPV…

Previously if a non-void function implictly returned, a dummy variable
was created as return value. Now instead it returns the result of the
OpUndef instruction. This better conveys the presence of undefined
behavior to SPIR-V consuming tools (and humans).

It also saves one ID per occurrence...

There will be subsequent commits to refine semantics, esp. version-specific semantics,
as well as I/O functionality and restrictions.

Note: I'm getting white-space differences in the preprocessor test results,
which I'm not checking in.  I think they need to be tagged as binary or something.