[gdb/testsuite] Fix regression in step-indirect-call-thunk.exp with gcc 7

Since commit 43127ae5714 ("Fix gdb.base/step-indirect-call-thunk.exp") I run
into:
...
gdb compile failed, gcc: error: unrecognized command line option \
  '-fcf-protection=none'; did you mean '-flto-partition=none'?
UNTESTED: gdb.base/step-indirect-call-thunk.exp: failed to prepare
...

The problem is that -fcf-protection is supported starting gcc 8, but I'm using
system gcc 7.5.0.

Fix this by only adding -fcf-protection=none for gcc 8 and later.

Tested on x86_64-linux, with gcc 7.5.0, 8.2.1 and 12.1.1.

1 files changed, 5 insertions, 1 deletions

diff --git a/gdb/testsuite/gdb.base/step-indirect-call-thunk.exp b/gdb/testsuite/gdb.base/step-indirect-call-thunk.exp
index 7c1b53c..c4f69ad 100644
--- a/gdb/testsuite/gdb.base/step-indirect-call-thunk.exp
+++ b/gdb/testsuite/gdb.base/step-indirect-call-thunk.exp
@@ -19,7 +19,11 @@ if { ![istarget "x86*"] } {
     return
 }
 
-set cflags "-mindirect-branch=thunk -mfunction-return=thunk -fcf-protection=none"
+set cflags "-mindirect-branch=thunk -mfunction-return=thunk"
+
+if { [gcc_major_version] >= 8 } {
+    append cflags " -fcf-protection=none"
+}
 if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
         [list debug "additional_flags=$cflags"]] } {
     return -1