--- htslib/Makefile.orig	2016-09-16 15:40:03 UTC
+++ htslib/Makefile
@@ -22,13 +22,13 @@
 # FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 # DEALINGS IN THE SOFTWARE.
 
-CC     = gcc
-AR     = ar
-RANLIB = ranlib
+CC     ?= gcc
+AR     ?= ar
+RANLIB ?= ranlib
 
 CPPFLAGS =
 # TODO: probably update cram code to make it compile cleanly with -Wc++-compat
-CFLAGS   = -g -Wall -O2
+CFLAGS   ?= -g -Wall -O2
 EXTRA_CFLAGS_PIC = -fpic
 LDFLAGS  =
 LIBS     =
