Use -Wno-sign-conversion if g++ is secretly clang

Makefile

@@ -77,6 +77,12 @@ FULL_SUBMITFILE = fullsubmit.tar.gz
 #Default Flags
 CXXFLAGS = -std=c++14 -Wconversion -Wall -Werror -Wextra -pedantic 
 
+# Disable -Wsign-conversion if using clang behind the scenes
+CLANG_VERSION = $(shell { g++ --version ; } 2>&1 | grep clang)
+ifneq "$(CLANG_VERSION)" ""
+	CXXFLAGS += -Wno-sign-conversion
+endif
+
 # make release - will compile "all" with $(CXXFLAGS) and the -O3 flag
 #				 also defines NDEBUG so that asserts will not check
 release: CXXFLAGS += -O3 -DNDEBUG