fix obvious problem with compiler.c and compiler.cc: for xlc, used 'regsub',

but for get_compiler_info, line must start with 'set'.

gdb/testsuite/lib/compiler.c

@@ -68,5 +68,5 @@ set compiler_info [join {hpacc __HP_aCC} -]
 #if defined (__xlc__)
 /* IBM'x xlc compiler. NOTE:  __xlc__ expands to a double quoted string of four
    numbers seperated by '.'s: currently "7.0.0.0" */
-regsub -all {\.} [join {xlc __xlc__} -] - compiler_info
+set need_a_set [regsub -all {\.} [join {xlc __xlc__} -] - compiler_info]
 #endif

gdb/testsuite/lib/compiler.cc

@@ -56,5 +56,5 @@ set compiler_info [join {hpacc __HP_aCC} -]
 #if defined (__xlc__)
 /* IBM'x xlc compiler. NOTE:  __xlc__ expands to a double quoted string of four
    numbers seperated by '.'s: currently "7.0.0.0" */
-regsub -all {\.} [join {xlc __xlc__} -] - compiler_info
+set need_a_set [regsub -all {\.} [join {xlc __xlc__} -] - compiler_info]
 #endif