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

[Tom de Vries]

Hi,

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.

Committed to trunk.

Thanks,
- Tom

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

---
 gdb/testsuite/gdb.base/step-indirect-call-thunk.exp |  6 +++++-
 gdb/testsuite/lib/gdb.exp                           | 11 +++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.base/step-indirect-call-thunk.exp b/gdb/testsuite/gdb.base/step-indirect-call-thunk.exp
index 7c1b53c99be..c4f69adc9b2 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
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 698dd14504e..5d6f1266b0f 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -8529,6 +8529,17 @@ gdb_caching_proc supports_gnuc {
     return [gdb_simple_compile $me $src object ""]
 }
 
+# Return 1 if compiler supports __GNUC__, otherwise return 0.
+gdb_caching_proc supports_gnuc {
+    set me "supports_gnuc"
+    set src {
+	#ifndef __GNUC__
+	#error "No gnuc"
+	#endif
+    }
+    return [gdb_simple_compile $me $src object ""]
+}
+
 # Return 1 if target supports mpx, otherwise return 0.
 gdb_caching_proc have_mpx {
     global srcdir