Add make variable NOOPT to disable optimization flags

This is used by Debian to build an unoptimized variant for debugging.

Make.inc

@@ -45,7 +45,11 @@ ifeq ($(ARCH),mingw32)
 $(error "the mingw32 compiler you are using fails the openblas testsuite. please see the Julia README.windows.md document for a replacement")
 endif
 
-CFLAGS_add += -std=c99 -Wall -O3 -I$(OPENLIBM_HOME) -I$(OPENLIBM_HOME)/include -I$(OPENLIBM_HOME)/ld80 -I$(OPENLIBM_HOME)/$(ARCH) -I$(OPENLIBM_HOME)/src -DASSEMBLER -D__BSD_VISIBLE -Wno-implicit-function-declaration
+CFLAGS_add += -std=c99 -Wall -I$(OPENLIBM_HOME) -I$(OPENLIBM_HOME)/include -I$(OPENLIBM_HOME)/ld80 -I$(OPENLIBM_HOME)/$(ARCH) -I$(OPENLIBM_HOME)/src -DASSEMBLER -D__BSD_VISIBLE -Wno-implicit-function-declaration
+
+ifneq ($(NOOPT),1)
+CFLAGS_add += -O3
+endif
 
 default: all