bpo-46600: ./configure --with-pydebug uses -Og with clang (GH-31052)

Fix the test checking if the C compiler supports -Og option in the
./configure script to also use -Og on clang which supports it.

Author: vstinner

Misc/NEWS.d/next/Build/2022-02-01-14-07-37.bpo-46600.NNLnfj.rst

@@ -0,0 +1,3 @@
+Fix the test checking if the C compiler supports ``-Og`` option in the
+``./configure`` script to also use ``-Og`` on clang which supports it. Patch
+by Victor Stinner.

configure

@@ -1791,6 +1791,28 @@ case $CC in
         fi
 esac
 
+# Check if CC supports -Og optimization level
+_SAVE_VAR([CFLAGS])
+CFLAGS="-Og"
+AC_CACHE_CHECK([if $CC supports -Og optimization level],
+               [ac_cv_cc_supports_og],
+  AC_COMPILE_IFELSE(
+    [
+      AC_LANG_PROGRAM([[]], [[]])
+    ],[
+      ac_cv_cc_supports_og=yes
+    ],[
+      ac_cv_cc_supports_og=no
+    ])
+)
+_RESTORE_VAR([CFLAGS])
+
+# Optimization messes up debuggers, so turn it off for
+# debug builds.
+PYDEBUG_CFLAGS="-O0"
+AS_VAR_IF([ac_cv_cc_supports_og], [yes],
+          [PYDEBUG_CFLAGS="-Og"])
+
 # tweak OPT based on compiler and platform, only if the user didn't set
 # it on the command line
 AC_SUBST(OPT)
@@ -1816,13 +1838,7 @@ then
 	case $ac_cv_prog_cc_g in
 	yes)
 	    if test "$Py_DEBUG" = 'true' ; then
-		# Optimization messes up debuggers, so turn it off for
-		# debug builds.
-                if "$CC" -v --help 2>/dev/null |grep -- -Og > /dev/null; then
-                    OPT="-g -Og -Wall"
-                else
-                    OPT="-g -O0 -Wall"
-                fi
+		OPT="-g $PYDEBUG_CFLAGS -Wall"
 	    else
 		OPT="-g $WRAP -O3 -Wall"
 	    fi