x11-toolkits/fltk: the port had been improved (+)

• Add an option to enable limited Cairo rendering support
• Do not strip static libraries upon installation as this breaks linking against them (the case for `x11/flruler')
• Restore files/patch-src_Makefile' which was ditched in r447379 (commit 2a288980b3dd) in favor of post-install' target because of the above and now this code is mature enough and should be less fragile to patch statically
• Garbage-collect no longer useful patch added in r138020 (commit 2a70195a3279) back in 2005 which now makes `-lm' appear twice in the fltk-config(1)'s LDFLAGS outputs
• Shorten local variable name in the `post-patch' target

Reported by: pkg-fallout