Fix Darwin build.

The recent changes to strip harder on Linux broke Darwin, which
doesn't have those options.
diff --git a/configure b/configure
index dedc977..af8e113 100755
--- a/configure
+++ b/configure
@@ -33,7 +33,14 @@
 # you call scripts/make.sh and friends directly.
 
 [ -z "$CC" ] && CC=cc
-[ -z "$STRIP" ] && STRIP="strip -s -R .note* -R .comment"
+
+# Strip harder on Linux.
+# Darwin's strip doesn't have equivalents of the binutils -s or -R.
+[ -z "$STRIP" ] && STRIP=strip
+if [ "$(uname)" != "Darwin" ]
+then
+  [ -z "$STRIP" ] && STRIP="strip -s -R .note* -R .comment"
+fi
 
 # If HOSTCC needs CFLAGS or LDFLAGS, just add them to the variable
 # ala HOSTCC="blah-cc --static"