physfs: Fix build with OS X 10.7's old clang

Closes: https://trac.macports.org/ticket/56077

devel/physfs/Portfile

@@ -27,6 +27,8 @@ checksums           rmd160  3d5e1f224b510444fe88247db10976e45d5302e8 \
 
 depends_lib-append  port:zlib port:readline port:ncurses
 
+patchfiles      objectAtIndex.patch
+
 livecheck.type  regex
 livecheck.url   [lindex ${master_sites} 0]LATEST_VERSION.html
 livecheck.regex ${name}-(\\d+(?:\\.\\d+)*)

devel/physfs/files/objectAtIndex.patch

@@ -0,0 +1,13 @@
+Fix build on OS X 10.7
+http://icculus.org/pipermail/physfs/2018-March/001255.html
+--- src/physfs_platform_apple.m.old	2018-03-20 11:30:49.000000000 -0600
++++ src/physfs_platform_apple.m	2018-03-20 11:31:12.000000000 -0600
+@@ -50,7 +50,7 @@
+     {
+         NSArray *paths = NSSearchPathForDirectoriesInDomains(NSApplicationSupportDirectory, NSUserDomainMask, TRUE);
+         BAIL_IF(!paths, PHYSFS_ERR_OS_ERROR, NULL);
+-        NSString *path = (NSString *) paths[0];
++        NSString *path = (NSString *) [paths objectAtIndex:0];
+         BAIL_IF(!path, PHYSFS_ERR_OS_ERROR, NULL);
+         size_t len = [path lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
+         const size_t applen = strlen(app);