build: Fix gcc-cross-x86_64-w64-mingw32-10.3.0 in Guix

Author: hebasto

contrib/guix/manifest.scm

@@ -162,13 +162,17 @@ desirable for building Bitcoin Core release binaries."
 (define (make-gcc-with-pthreads gcc)
   (package-with-extra-configure-variable gcc "--enable-threads" "posix"))
 
+;; Required to support std::filesystem for mingw-w64 target.
+(define (make-gcc-without-newlib gcc)
+  (package-with-extra-configure-variable gcc "--with-newlib" "no"))
+
 (define (make-mingw-pthreads-cross-toolchain target)
   "Create a cross-compilation toolchain package for TARGET"
   (let* ((xbinutils (cross-binutils target))
          (pthreads-xlibc mingw-w64-x86_64-winpthreads)
          (pthreads-xgcc (make-gcc-with-pthreads
                          (cross-gcc target
-                                    #:xgcc (make-ssp-fixed-gcc base-gcc)
+                                    #:xgcc (make-gcc-without-newlib (make-ssp-fixed-gcc base-gcc))
                                     #:xbinutils xbinutils
                                     #:libc pthreads-xlibc))))
     ;; Define a meta-package that propagates the resulting XBINUTILS, XLIBC, and