Fix warnings/errors for strict aliasing & function prototypes

This fixes various issues related to gcc's strict-aliasing warning
by using unions. It also handles various cases hit with
gcc's missing-declarations warning.

glslang/MachineIndependent/PoolAlloc.cpp

@@ -190,7 +190,7 @@ void TAllocation::checkGuardBlock(unsigned char*, unsigned char, const char*) co
 #endif
 {
 #ifdef GUARD_BLOCKS
-    for (int x = 0; x < guardBlockSize; x++) {
+    for (size_t x = 0; x < guardBlockSize; x++) {
         if (blockMem[x] != val) {
             const int maxSize = 80;
             char assertMsg[maxSize];