Use require !skip_ctf_tests

This changes some tests to use "require !skip_ctf_tests".

gdb/testsuite/gdb.base/ctf-constvars.exp

@@ -24,10 +24,7 @@
 #            const pointers to const vars
 # with mixed types.
 
-if [skip_ctf_tests] {
-    unsupported "no CTF debug format support, or CTF disabled in GDB"
-    return 0
-}
+require !skip_ctf_tests
 
 standard_testfile .c
 

gdb/testsuite/gdb.base/ctf-ptype.exp

@@ -15,10 +15,7 @@
 
 # This file is a subset of ptype.exp written by Rob Savoye. (rob@cygnus.com)
 
-if [skip_ctf_tests] {
-    unsupported "no CTF debug format support, or CTF disabled in GDB"
-    return 0
-}
+require !skip_ctf_tests
 
 # Some tests require GCC.
 set gcc_compiled [is_c_compiler_gcc]

gdb/testsuite/gdb.ctf/cross-tu-cyclic.exp

@@ -15,10 +15,7 @@
 
 # This file is a subset of ptype.exp written by Rob Savoye. (rob@cygnus.com)
 
-if [skip_ctf_tests] {
-    unsupported "no CTF debug format support, or CTF disabled in GDB"
-    return 0
-}
+require !skip_ctf_tests
 
 standard_testfile cross-tu-cyclic-1.c  cross-tu-cyclic-2.c \
 	cross-tu-cyclic-3.c  cross-tu-cyclic-4.c

gdb/testsuite/gdb.ctf/funcreturn.exp

@@ -13,10 +13,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-if [skip_ctf_tests] {
-    unsupported "no CTF debug format support, or CTF disabled in GDB"
-    return 0
-}
+require !skip_ctf_tests
 
 if [target_info exists no_long_long] {
     set exec_opts [list debug additional_flags=-DNO_LONG_LONG]

gdb/testsuite/gdb.ctf/multi.exp

@@ -15,10 +15,7 @@
 
 # This file is a subset of ptype.exp written by Rob Savoye. (rob@cygnus.com)
 
-if [skip_ctf_tests] {
-    unsupported "no CTF debug format support, or CTF disabled in GDB"
-    return 0
-}
+require !skip_ctf_tests
 
 standard_testfile ctf-a.c ctf-b.c ctf-c.c