Fix some compiler warnings

This change primarily fixes some -Wconversion warnings from gcc, but
also silences a warning triggered in glslang_tab.cpp, which is generated
code from bison.

There are still several GCC conversion warnings in Types.h due to the
use of bit fields that will be resolved in a future change.

SPIRV/doc.h

@@ -240,8 +240,8 @@ public:
     OperandParameters operands;
 
 protected:
-    int typePresent   : 1;
-    int resultPresent : 1;
+    bool typePresent   : 1;
+    bool resultPresent : 1;
 };
 
 // The set of objects that hold all the instruction/operand