partial bitcoin#30511: GCC 12 consolidation

excludes:
- 8b41ede

contrib/guix/manifest.scm

@@ -28,6 +28,7 @@
              (guix build-system gnu)
              (guix build-system python)
              (guix build-system trivial)
+             (guix download)
              (guix gexp)
              (guix git-download)
              ((guix licenses) #:prefix license:)
@@ -94,7 +95,18 @@ chain for " target " development."))
       (home-page (package-home-page xgcc))
       (license (package-license xgcc)))))
 
-(define base-gcc gcc-12)
+(define base-gcc
+  (package
+    (inherit gcc-12) ;; 12.3.0
+    (version "12.4.0")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "mirror://gnu/gcc/gcc-"
+                                  version "/gcc-" version ".tar.xz"))
+              (sha256
+               (base32
+                "0xcida8l2wykvvzvpcrcn649gj0ijn64gwxbplacpg6c0hk6akvh"))))))
+
 (define base-linux-kernel-headers linux-libre-headers-6.1)
 
 (define* (make-bitcoin-cross-toolchain target
@@ -122,7 +134,10 @@ desirable for building Dash Core release binaries."
 (define (make-mingw-pthreads-cross-toolchain target)
   "Create a cross-compilation toolchain package for TARGET"
   (let* ((xbinutils (binutils-mingw-patches (cross-binutils target)))
-         (pthreads-xlibc mingw-w64-x86_64-winpthreads)
+         (machine (substring target 0 (string-index target #\-)))
+         (pthreads-xlibc (make-mingw-w64 machine
+                                         #:xgcc (cross-gcc target #:xgcc (gcc-mingw-patches base-gcc))
+                                         #:with-winpthreads? #t))
          (pthreads-xgcc (cross-gcc target
                                     #:xgcc (gcc-mingw-patches mingw-w64-base-gcc)
                                     #:xbinutils xbinutils