Merge bitcoin/bitcoin#30511: guix: GCC 12 consolidation

d1592d2eee guix: use gcc-12 to compile winpthreads (fanquake)
b23690e821 guix: use GCC 12.4.0 over 12.3.0 (fanquake)
8b41ede55e guix: consolidate back to GCC 12 toolchain for all HOSTS (fanquake)

Pull request description:

  This PR contains 3 changes:

  * Bump GCC in Guix from [12.3.0 to 12.4.0](https://gcc.gnu.org/gcc-12/). A patch was sent upstream, https://lists.gnu.org/archive/html/guix-patches/2024-06/msg01025.html, but has not landed.
  * Consolidate all build environments back to using a GCC 12 toolchain. After #21778, the macOS environment is no-longer pinned to 11 (12 would otherwise cause issues building cctools). So, instead of requiring all builders to compile an additional GCC toolchain, use 12.
  * Use GCC 12 to compile winpthreads. Currently, GCC 11 is used; which became apparent in https://github.com/bitcoin/bitcoin/pull/30452#issuecomment-2244715566.

ACKs for top commit:
  TheCharlatan:
    ACK d1592d2eee
  hebasto:
    ACK d1592d2eee.

Tree-SHA512: e3aa1fa3e69500c93180e07cb4684661247ec6bc45245f746538d81406ff1d8777131590307496dda3287a112b6633e4991168586ca4c2036fa3a57b1efa9c87

contrib/guix/manifest.scm

@@ -25,6 +25,7 @@
              (guix build-system gnu)
              (guix build-system python)
              (guix build-system trivial)
+             (guix download)
              (guix gexp)
              (guix git-download)
              ((guix licenses) #:prefix license:)
@@ -91,7 +92,18 @@ 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
@@ -119,7 +131,10 @@ desirable for building Bitcoin 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
@@ -500,6 +515,7 @@ inspecting signatures in Mach-O binaries.")
         gzip
         xz
         ;; Build tools
+        gcc-toolchain-12
         cmake-minimal
         gnu-make
         libtool
@@ -515,22 +531,16 @@ inspecting signatures in Mach-O binaries.")
         python-lief)
   (let ((target (getenv "HOST")))
     (cond ((string-suffix? "-mingw32" target)
-           (list ;; Native GCC 12 toolchain
+           (list zip
-                 gcc-toolchain-12
-                 zip
                  (make-mingw-pthreads-cross-toolchain "x86_64-w64-mingw32")
                  nsis-x86_64
                  nss-certs
                  osslsigncode))
           ((string-contains target "-linux-")
-           (list ;; Native GCC 12 toolchain
+           (list (list gcc-toolchain-12 "static")
-                 gcc-toolchain-12
-                 (list gcc-toolchain-12 "static")
                  (make-bitcoin-cross-toolchain target)))
           ((string-contains target "darwin")
-           (list ;; Native GCC 11 toolchain
+           (list clang-toolchain-18
-                 gcc-toolchain-11
-                 clang-toolchain-18
                  lld-18
                  (make-lld-wrapper lld-18 #:lld-as-ld? #t)
                  python-signapple