msys2-runtime: upgrade to v3.4.6

This corresponds to
git-for-windows/msys2-runtime#50.

The `update-patches.sh` script had to be adjusted to reflect that Cygwin
changed its tag naming scheme. Before, it was `cygwin-<version>-release`
where the version had underscores instead of dots. Now, it is
`cygwin-<version>` with dots, not underscores. Also, the source URL
changed to `git+https` but we obviously cannot clone from such a URL.

Signed-off-by: Johannes Schindelin <[email protected]>

msys2-runtime/0002-Fix-msys-library-name-in-import-libraries.patch

@@ -1,4 +1,4 @@
-From e78e1440c29bc5340ef5403af120a3101e11361d Mon Sep 17 00:00:00 2001
+From e6c92c6eaf63d328b94f7942a1173c2adb63f1f1 Mon Sep 17 00:00:00 2001
 From: Kaleb Barrett <[email protected]>
 Date: Sun, 14 Mar 2021 18:58:55 -0500
 Subject: [PATCH 02/N] Fix msys library name in import libraries
@@ -9,14 +9,14 @@ rename the output file name from `cygwin1.dll` to `msys-2.0.dll`.
 Let's preemptively fix up all the import libraries that would link
 against `msys_2_0.dll` to correctly link against `msys-2.0.dll` instead.
 ---
- winsup/cygwin/speclib | 1 +
+ winsup/cygwin/scripts/speclib | 1 +
  1 file changed, 1 insertion(+)
 
-diff --git a/winsup/cygwin/speclib b/winsup/cygwin/speclib
-index b900960..617a9c2 100755
---- a/winsup/cygwin/speclib
-+++ b/winsup/cygwin/speclib
-@@ -37,6 +37,7 @@ while (<$nm_fd>) {
+diff --git a/winsup/cygwin/scripts/speclib b/winsup/cygwin/scripts/speclib
+index e6d4d8e..4dcadcb 100755
+--- a/winsup/cygwin/scripts/speclib
++++ b/winsup/cygwin/scripts/speclib
+@@ -38,6 +38,7 @@ while (<$nm_fd>) {
      study;
      if (/ I _?(.*)_dll_iname/o) {
  	$dllname = $1;