t7800: configure $(pwd) for posix-paths on MINGW

In test #49, $(pwd) must match $(readlink), which is an MSys utility.

Signed-off-by: Karsten Blees <blees@dcon.de>

t/t7800-difftool.sh

@@ -10,6 +10,14 @@ Testing basic diff tool invocation
 
 . ./test-lib.sh
 
+if test_have_prereq MINGW
+then
+	# Avoid posix-to-windows path mangling
+	pwd () {
+		builtin pwd
+	}
+fi
+
 difftool_test_setup ()
 {
 	test_config diff.tool test-tool &&