Trac #34293: rubiks: Work around build failure with XCode

On Apple clang version 13.1.6 (clang-1316.0.21.2.5), building `g++
-std=gnu++11 -g -O2  -c mcube.cpp` appears to hang forever.

We work around this by reducing the optimization level on macOS.

URL: https://trac.sagemath.org/34293
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): John Palmieri

build/pkgs/rubiks/spkg-install.in

@@ -2,14 +2,6 @@
 ## rubiks
 ###########################################
 
-# Work around a bug in gcc 4.6.0: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48702
-if [ "`testcc.sh $CC`" = GCC ] ; then
-    if $CC -dumpversion 2>/dev/null |grep >/dev/null '^4\.6\.[01]$' ; then
-        echo "Warning: Working around bug in gcc 4.6.0"
-        EXTRA_FLAG="-fno-ivopts"
-    fi
-fi
-
 # Most packages do not need all these set
 # But it is better to do them all each time, rather than ommit
 # a flag by mistake.
@@ -50,6 +42,11 @@ else
     INSTALL=install; export INSTALL
 fi
 
+if [ $UNAME = "Darwin" ]; then
+    # #34293: Work around compiler hang
+    export CXXFLAGS="$CXXFLAGS -O1"
+fi
+
 cd src
 
 echo "Building Rubiks cube solvers"