fix compiler detection

Reducibility_Multiplex/Makefile

@@ -4,20 +4,20 @@ LDFLAGS=-lm -lgmp -lz
 
 HAVE_CC=$(shell $(CC) --version ; echo \$?)
 
-IS_CC_GCC=$(shell $(CC) --version | grep -Eic 'gcc' || echo "0")
-IS_CC_CLANG=$(shell $(CC) --version | grep -Eic '(llvm|clang)' || echo "0") 
-IS_CC_ICC=$(shell $(CC) --version | grep -Eic 'Intel' || echo "0")
+IS_CC_GCC=$(shell $(CC) --version | grep -Eic 'gcc' || echo "NUL")
+IS_CC_CLANG=$(shell $(CC) --version | grep -Eic '(llvm|clang)' || echo "NUL") 
+IS_CC_ICC=$(shell $(CC) --version | grep -Eic 'Intel' || echo "NUL")
 
 
-ifeq ($(IS_CC_GCC), 1)
+ifneq ($(IS_CC_GCC),"NUL")
 # compiler is GCC
 	CFLAGS+=-fopenmp
 else
-    ifeq ($(IS_CC_CGLANG), 1)
+    ifneq ($(IS_CC_CGLANG), "NUL")
 # compiler is CLANG
 	LDFLAGS+=-lomp
     else 
-         ifeq ($(IS_CC_ICC), 1)
+         ifneq ($(IS_CC_ICC), "NUL")
 # compiler is Intel icc
 		CFLAGS+=-qopenmp
          endif