The DiagnosticStream will not emit the accumulated message
text if the error is SPV_FAILED_MATCH.
Change various interfaces to accept the intended error
code instead of a boolean "is_optional". This allows
us to avoid repeating the following type of logic deep
inside helper methods:
if (is_optional) return SPV_FAILED_MATCH;
return diagnostic() << " message text ";
Use this to shorten error return code in the assembler.
For example, change this:
if (error = something()) {
diagnostic() << " Bad integer literal " << value;
return SPV_ERROR_INVALID_VALUE;
}
to this:
if (error = something())
return diagnostic() << " Bad integer literal " << value;
Also shorten code due to the fact that binaryEncodeU32 and
binaryCodeU64 can't fail (short of failure to expand a std::vector).
