[PATCH hints/darwin.sh] Don't override user-specified optimize flag

hints/darwin.sh contains the assignment:
	optimize='-O3'

So if I follow the instructions in INSTALL and run
	sh ./Configure -Doptimize=-g
in order to build a debugging perl, it won't work.
Instead it's necessary to write:
	sh ./Configure -Adefine:optimize=-g

I toyed with changing the documentation in INSTALL, but I can't see
any reason why the hints file should over-ride the user here. So I
changed hints/darwin.sh as below.

 .robin.

--- hints/darwin.sh.orig	Sun Jul 15 18:02:54 2001
+++ hints/darwin.sh	Sun Jul 15 18:18:03 2001
@@ -41,7 +41,9 @@
 #libc='/usr/lib/libSystem.dylib';
 
 # Optimize.
-optimize='-O3';
+if [ "x$optimize" = 'x' ]; then
+    optimize='-O3'
+fi
 
 # We have a prototype for telldir.
 ccflags="${ccflags} -pipe -fno-common -DHAS_TELLDIR_PROTOTYPE";

• [PATCH hints/darwin.sh] Don't override user-specified optimize flag by Robin Houston
• Re: Don't override user-specified optimize flag by H.Merijn Brand