Provide both signed and unsigned int variants of bitcode-based builtins.

When creating function Symbols for functions that were defined in LLVM bitcode for the standard library, if any of the function parameters are integer types, create two ispc-side Symbols: one where the integer types are all signed and the other where they are all unsigned.  This allows us to provide, for example, both store_to_int16(reference int a[], uniform int offset, int val) as well as store_to_int16(reference unsigned int a[], uniform int offset, unsigned int val). functions.

Added some additional tests to exercise the new variants of these.

Also fixed some cases where the __{load,store}_int{8,16} builtins would read from/write to memory even if the mask was all off (which could cause crashes in some cases.)

Makefile

@@ -6,12 +6,9 @@ ARCH_OS = $(shell uname)
 ARCH_TYPE = $(shell arch)
 
 CLANG=clang
-CLANG_LIBS = -lclangFrontendTool -lclangFrontend -lclangDriver \
-             -lclangSerialization -lclangCodeGen -lclangParse -lclangSema \
-             -lclangStaticAnalyzerFrontend -lclangStaticAnalyzerCheckers \
-             -lclangStaticAnalyzerCore \
-             -lclangAnalysis -lclangIndex -lclangRewrite \
-             -lclangAST -lclangLex -lclangBasic
+CLANG_LIBS = -lclangFrontend -lclangDriver \
+             -lclangSerialization -lclangParse -lclangSema \
+             -lclangAnalysis -lclangAST -lclangLex -lclangBasic
 
 LLVM_LIBS=$(shell llvm-config --ldflags --libs) -lpthread -ldl
 LLVM_CXXFLAGS=$(shell llvm-config --cppflags)