pacman: use the private MSYS root on Windows

Author: frangarcj

patches/pacman/0001-allow-writable-non-root-installation-roots.patch

@@ -6,10 +6,10 @@ for alternate roots the caller cannot write. When extracting as a non-root
 user, preserve the package permissions but let the filesystem assign the
 caller's UID and GID instead of attempting a privileged chown.
 
-MSYS has no Unix privilege boundary and cannot reliably apply access(2) to a
-Win32 path supplied by the native frontend. There, accept only an explicit
-alternate root and let the transaction's filesystem operations reject a path
-the current Windows user cannot write.
+MSYS has no Unix privilege boundary, and the private runtime maps the SDK
+directory itself to POSIX `/`. There, omit the Unix root-user check just as the
+MSYS2 port does; the process has only the invoking Windows user's filesystem
+rights and extraction rejects paths that user cannot write.
 
 Based on pacman 7.1.0 commit 5683f8477a0afcc6b331766175a83445b2dcfe89.
 
@@ -45,12 +45,12 @@ Based on pacman 7.1.0 commit 5683f8477a0afcc6b331766175a83445b2dcfe89.
 
 +static int has_writable_alternate_root(void)
 +{
++#if defined(__MSYS__) || defined(__CYGWIN__)
++	return 1;
++#else
 +	if(config->rootdir == NULL || strcmp(config->rootdir, "/") == 0) {
 +		return 0;
 +	}
-+#ifdef __MSYS__
-+	return 1;
-+#else
 +	return access(config->rootdir, W_OK | X_OK) == 0;
 +#endif
 +}