Merge pull request devitocodes#1263 from devitocodes/smarter-custom-c…

…ompiler

jit: Smarter CustomCompiler

devito/compiler.py

@@ -489,9 +489,12 @@ def __init__(self, *args, **kwargs):
 
 
 class CustomCompiler(Compiler):
+
     """
     Custom compiler based on standard environment flags.
 
+    If no environment flags are found, defaults to the GNUCompiler.
+
     Notes
     -----
     Currently honours CC, CFLAGS and LDFLAGS, with defaults similar to the
@@ -500,6 +503,14 @@ class CustomCompiler(Compiler):
     or otherwise default to ``-fopenmp``.
     """
 
+    def __new__(cls, *args, **kwargs):
+        if any(i in environ for i in ['CC', 'CXX', 'CFLAGS', 'LDFLAGS']):
+            obj = super().__new__(cls, *args, **kwargs)
+            obj.__init__(*args, **kwargs)
+            return obj
+        else:
+            return GNUCompiler(*args, **kwargs)
+
     def __init__(self, *args, **kwargs):
         super(CustomCompiler, self).__init__(*args, **kwargs)