Fix pgc compilation with --disable-optimizations.

-O1 disables dead code elimination on pgc, use -O instead.

configure

@@ -2806,7 +2806,7 @@ probe_cc(){
         opt_common='-alias=ansi -Mdse -Mlre -Mpre'
         _cflags_speed="-O3 -Mautoinline -Munroll=c:4 $opt_common"
         _cflags_size="-O2 -Munroll=c:1 $opt_common"
-        _cflags_noopt="-O1"
+        _cflags_noopt="-O"
         _flags_filter=pgi_flags
     elif $_cc 2>&1 | grep -q Microsoft; then
         _type=msvc