[Darwin, testsuite] Update tests for common section use.

These two tests are explicitly testing the use of specific
sections or assembler directives for data that is placed in
common.  Append -fcommon to the flags to restore them.

gcc/testsuite/ChangeLog:

2019-11-21  Iain Sandoe  <iain@sandoe.co.uk>

	* gcc.dg/darwin-comm.c: Add -fcommon to compile flags.
	* gcc.dg/darwin-sections.c: Likewise.

From-SVN: r278596

gcc/testsuite/gcc.dg/darwin-comm.c

 /* { dg-do compile { target *-*-darwin[912]* } } */
+/* { dg-options "-fcommon" } */
 /* { dg-final { scan-assembler ".comm\[ \t\]_foo,1,15" } } */
 
 char foo __attribute__ ((aligned(32768)));

gcc/testsuite/gcc.dg/darwin-sections.c

 /* { dg-do compile {target *-*-darwin* } } */
-/* { dg-options "-std=c99 -w" } */
+/* { dg-options "-std=c99 -w -fcommon" } */
 
 /* This has been designed to give the same section usage for
    -m32 and -m64 - so don't put any ints or longs in it ... */