c6x: handle c6x unk_isa in TARGET_CPU_CPP_BUILTINS

Fixes all-gcc for c6x config-list.mk that complained about

error: enumeration value ‘unk_isa’ not handled in switch

Maybe seeing unk_isa in the cpu switch statement should
__builtin_abort() but be conservative to just allow all-gcc of config-list.mk
to compile

From-SVN: r222308

gcc/ChangeLog

 2015-04-22  Bernhard Reutner-Fischer  <aldot@gcc.gnu.org>
 
+	* config/c6x/c6x.h (TARGET_CPU_CPP_BUILTINS): Add unk_isa.
+
+2015-04-22  Bernhard Reutner-Fischer  <aldot@gcc.gnu.org>
+
 	* config/bfin/bfin.h (TARGET_CPU_CPP_BUILTINS): Add BFIN_CPU_UNKNOWN.
 
 2015-04-22  Hale Wang  <hale.wang@arm.com>

gcc/config/c6x/c6x.h

@@ -84,6 +84,8 @@ extern c6x_cpu_t c6x_arch;
 						\
       switch (c6x_arch)				\
 	{					\
+	case unk_isa:				\
+	  break;				\
 	case C6X_CPU_C62X:			\
 	  builtin_define ("_TMS320C6200");	\
 	  break;				\