cmssw-tool-conf: enable GDB also for Darwin/OSX

Patch enables GDB for Darwin/OSX. There is no technical reasons why
GDB should not work on Darwin/OSX. Users can use it with root privileges
or can code sign it with self-signed certificate.

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
git: clean install errors on Darwin/OSX

There are a number of errors from post-install script on Darwin/OSX.

Can't open osx108_amd64_gcc481/external/git/1.8.3.1-cms2/share/git-gui/lib/Git: No such file or directory, <> line 7902.
Can't open Gui.app/Contents/Info.plist: No such file or directory, <> line 7902.
Can't open osx108_amd64_gcc481/external/git/1.8.3.1-cms2/share/git-gui/lib/Git: No such file or directory, <> line 7902.
Can't open Gui.app/Contents/MacOS/Wish: No such file or directory, <> line 7902.
Can't open osx108_amd64_gcc481/external/git/1.8.3.1-cms2/share/git-gui/lib/Git: No such file or directory, <> line 7902.
Can't open Gui.app/Contents/Resources/git-gui.icns: No such file or directory, <> line 7902.
Can't open osx108_amd64_gcc481/external/git/1.8.3.1-cms2/share/git-gui/lib/Git: No such file or directory, <> line 7902.
Can't open Gui.app/Contents/Resources/Scripts/AppMain.tcl: No such file or directory, <> line 7902.
find: osx108_amd64_gcc481/external/git/1.8.3.1-cms2/lib64/perl5: No such file or directory

- Disable building Tcl/Tk `Git Gui.app` on Darwin/OSX.
- Treat lib64/perl5 and lib/perl5 equally in post-install script.
- No need to use -name "*" on find, it's default.

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>