fixed makefile to work correctly with travis

openmp-threading/Makefile

@@ -2,11 +2,9 @@
 # User Options
 #===============================================================================
 
-# Compiler options are "gnu", "llvm", and "intel".
-# This can be set below, or with the "COMPILER" environment variable.
-# Default is gnu.
-ifeq ($(COMPILER),)
-COMPILER  = gnu
+# Compiler can be set below, or via environment variable
+ifeq ($(CC),)
+CC        = gcc
 endif
 OPTIMIZE  = yes
 DEBUG     = no
@@ -32,24 +30,26 @@ obj = $(source:.c=.o)
 # Sets Flags
 #===============================================================================
 
+# Make sure we didn't pick up lower case cc
+ifeq (cc,$(CC))
+CC    = gcc
+endif
+
 # Standard Flags
 CFLAGS := -std=gnu99 -Wall
 
 # gcc Compiler
-ifeq ($(COMPILER),gnu)
-  CC = gcc
+ifneq (,$(findstring gcc,$(CC)))
   CFLAGS += -fopenmp -flto
 endif
 
 # LLVM Compiler
-ifeq ($(COMPILER),llvm)
-  CC = clang
+ifneq (,$(findstring clang,$(CC)))
   CFLAGS += -fopenmp -flto
 endif
 
-# intel compiler
-ifeq ($(COMPILER),intel)
-  CC = icc
+# Intel Compiler
+ifneq (,$(findstring intel,$(CC)))
   CFLAGS += -qopenmp -ipo
 endif