Cray: gcc -> cc (#826)

TYPE: enhancement

KEYWORDS: Cray, gcc, cc

SOURCE: Peter Johnsen and Patricia Balle (Cray, Inc.)

DESCRIPTION OF CHANGES: 
Change the default C compiler from gcc to cc, for the stanza
```
Cray XE and XC CLE/Linux x86_64, Cray CCE compiler
```

LIST OF MODIFIED FILES: 
M arch/configure.defaults

TESTS CONDUCTED: 
None required.

arch/configure.defaults

@@ -1282,7 +1282,7 @@ OMP             =       # -homp
 OMPCC           =       # -homp
 SFC             =       ftn $(NOOMP)
 SCC             =       cc 
-CCOMP           =       gcc 
+CCOMP           =       cc 
 DM_FC           =       ftn $(NOOMP)
 DM_CC           =       cc
 FC              =       $(DM_FC)