Compile pr79793-[12].c with -mtune=generic

pr79793-1.c and pr79793-2.c are failed when GCC is configured with
--with-cpu=slm since lea is used to adjust stack, instead of sub/add.
This patch uses -mtune=generic to always generate sub and add.

	* gcc.target/i386/pr79793-1.c: Compile with -mtune=generic.
	* gcc.target/i386/pr79793-2.c: Likewise.

From-SVN: r250745

gcc/testsuite/ChangeLog

+2017-07-31  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* gcc.target/i386/pr79793-1.c: Compile with -mtune=generic.
+	* gcc.target/i386/pr79793-2.c: Likewise.
+
 2017-07-31  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR target/25967

gcc/testsuite/gcc.target/i386/pr79793-1.c

 /* { dg-do compile { target { *-*-linux* && { ! ia32 } } } } */
-/* { dg-options "-O2 -mgeneral-regs-only" } */
+/* { dg-options "-O2 -mgeneral-regs-only -mtune=generic" } */
 
 void
  __attribute__ ((interrupt))

gcc/testsuite/gcc.target/i386/pr79793-2.c

 /* { dg-do compile { target { *-*-linux* && { ! ia32 } } } } */
-/* { dg-options "-O2 -mgeneral-regs-only" } */
+/* { dg-options "-O2 -mgeneral-regs-only -mtune=generic" } */
 
 typedef unsigned int uword_t __attribute__ ((mode (__word__)));