Don't try to compile scan cython code if no compiler. More robust if the c file isn't available.

theano/gof/lazylinker_c.py

@@ -89,11 +89,11 @@ except ImportError:
             if not os.path.exists(cfile):
                 # This can happen in not normal case. We just
                 # disable the c clinker. If we are here the user
-                # didn't disable the compiler, so print a warning.
+                # didn't disabled the compiler, so print a warning.
                 warnings.warn(
                     "The file lazylinker_c.c is not available. This do"
                     "not happen normally. You are probably in a strange"
-                    "setup. This mean Theano ca not use the cvm:"
+                    "setup. This mean Theano can not use the cvm:"
                     "our c execution engine for Theano function. If you"
                     "want to remove this warning, use the Theano flag"
                     "'cxx=' (set to an empty string) to disable all c"

theano/scan_module/scan_perform_ext.py

@@ -54,11 +54,27 @@ except ImportError:
             if version != getattr(scan_perform, '_version', None):
                 raise ImportError()
         except ImportError:
-
+            if not theano.config.cxx:
+                raise ImportError("no c compiler, can't compile cython code")
             _logger.info("Compiling C code for scan")
             dirname = 'scan_perform'
             cfile = os.path.join(theano.__path__[0], 'scan_module',
                                  'scan_perform.c')
+            if not os.path.exists(cfile):
+                # This can happen in not normal case. We just
+                # disable the cython code. If we are here the user
+                # didn't disabled the compiler, so print a warning.
+                warnings.warn(
+                    "The file scan_perform.c is not available. This do"
+                    "not happen normally. You are probably in a strange"
+                    "setup. This mean Theano can not use the cython code for "
+                    "scan. If you"
+                    "want to remove this warning, use the Theano flag"
+                    "'cxx=' (set to an empty string) to disable all c"
+                    "code generation."
+                )
+                raise ImportError("The file lazylinker_c.c is not available.")
+
                 code = open(cfile).read()
             loc = os.path.join(config.compiledir, dirname)
             if not os.path.exists(loc):