do not raise error where cygpath is not available

mesonbuild/modules/external_project.py

@@ -116,17 +116,19 @@ def _configure(self, state: 'ModuleState') -> None:
             configure_path = Path(self.src_dir, self.configure_command)
             configure_prog = state.find_program(configure_path.as_posix())
             configure_cmd = configure_prog.get_command()
-            # On Windows the configure command should be converted to
-            # unix style path by cygpath command,
+            # On Cygwin, MSYS2 and GitBash the configure command should be
+            # converted to unix style path by cygpath command,
             # because the colon in the drive letter breaks many configure scripts.
+            # Do nothing on other environment where cygpath is not available.
             if (
                 configure_path.drive
                 and len(configure_cmd) >= 2
                 and configure_cmd[-1] == configure_path.as_posix()
             ):
-                cygpath = state.find_program('cygpath').get_command()
-                _p, o, _e = Popen_safe(cygpath + [configure_cmd[-1]])
-                configure_cmd = configure_cmd[:-1] + [Path(o.strip("\n")).as_posix()]
+                cygpath = state.find_program('cygpath', required=False)
+                if cygpath.found():
+                    _p, o, _e = Popen_safe(cygpath.get_command() + [configure_cmd[-1]])
+                    configure_cmd = configure_cmd[:-1] + [Path(o.strip("\n")).as_posix()]
             workdir = self.build_dir
             self.make = state.find_program('make').get_command()