git-gui: fix detection of Cygwin

MSys2 might *look* like Cygwin, but it is *not* Cygwin... Unless it
is run with `MSYSTEM=MSYS`, that is.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

diff --git a/git-gui.sh b/git-gui.sh
index 11048c7..2381c3e 100755 (executable)
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -275,6 +275,10 @@ proc is_Cygwin {} {
                                set _iscygwin 0
                        } else {
                                set _iscygwin 1
+                               # Handle MSys2 which is only cygwin when MSYSTEM is MSYS.
+                               if {[info exists ::env(MSYSTEM)] && $::env(MSYSTEM) ne "MSYS"} {
+                                       set _iscygwin 0
+                               }
                        }
                } else {
                        set _iscygwin 0