Preprocessing line number handling

Everytime we switch to a new source string, the line are reset.
We need to reset lastLine and also output newlines appropriately.

SourceLineSynchronizer is added for keeping track of the last
line number and output newlines appropriately if we switch to
a new line in the preprocessor.

AST -> SPV testing: Update test for using new TbdFunctionality() that is non-fatal and uniquifies printed TBDs.

Only output explicit extension directives in preprocessing.

spv::Builder::Loop constructor inits all members.

After construction, the Loop is effectively const.

This perturbs the IDs in SPIR-V tests because the body block
is created before generating any of the loop code, rather than
only when the body is first referenced.

Issue #28: Correctly handle a single input argument conversion when the input argument is an aggregate.

Preprocessing output shouldn't contain extensions enabled as
dependencies.

Generate correctly structured do-while loops.

Fix g++ build break (portibility problems with stl hash).  This partly turns off the stl improvements.

It also removes some old code that ancient compilers used to need.
However, the main issue is getting access to hash functions for
unordered_map in portable way.

Preprocessor: 1) Rationalize the "fixed atom" scheme, 2) remove redundant lookups when the text is already available.

This simplification is a prelude to eliminating what I appear unnecessary
symbol inserts into tables when tokenizing in the preprecessor, which
show up as taking notable time. (Performance issue.)  It also simply makes
the preprocessor easier to understand, which it is badly in need of.

Front-end: Add error-recovery code for a switch statement that ends with a case/default that has no statements.

The loop test is always emitted before the loop body.

For do-while loops, use a phi node to track whether we're
on the first loop iteration, and only check the loop test
on the second and subsequent iterations.

For do-while loops, the loop test branch no longer occurs
at the top of the loop, so it must get its own selection
merge instruction.

A block can't be the target of more than one merge instruction.
So when the loop test executes after the body (as in do-while in GLSL)
we need to introduce a dummy block to be the target of the selection
merge just before the loop test conditional branch.

The other arm of the branch exits the loop and hence is the
"break block" exception in the structured control flow rules.

Added a setStringsWithLengths() method to TShader.

Removed the single usage of exceptions in all of glslang.

This allows us to pass through non null-terminated strings.

Comment out some dead assignments per suggestion from static analysis…

Code is left in as comments for clarity to humans.

Protect location setting methods from writing to non-existing strings.

TInputScanner advances its internal indices to the next character at
the end of get(), which means, after reading in the last character
in the user-provided shader string, internal index (currentSource)
will point to the next shader string (currentSource == numSources),
which doesn't exist. Then if a location setting method is called,
we will write to some out-of-bound memory.

A test case for this is "#line 10000\n". The eval() method in CPPline()
will evaluate 10000, but at the same time it reads in the next
token, '\n', and the currentSource will be numSources in TInputScanner.
Then a parseContext.setCurrentLine() is called, we are writing to
out-of-bound memory. Another test case will be "#line 10000 0\n".