guix: remove gcc-toolchain static from Windows build

The libs in this dir are the following:
```bash
ls /gnu/store/2vnbkrdin4rrf7ygnr80mlcglin4qqa4-gcc-toolchain-12.3.0-static/lib/lib
libanl.a           libc.a             libdl.a         libm.a
libBrokenLocale.a  libcrypt.a         libg.a          libmcheck.a
libpthread.a       librt.a
libresolv.a        libutil.a
```

These do not need to be propogated into the Windows build environment.

Author: fanquake

contrib/guix/libexec/build.sh

@@ -75,9 +75,8 @@ export OBJC_INCLUDE_PATH="${NATIVE_GCC}/include"
 export OBJCPLUS_INCLUDE_PATH="${NATIVE_GCC}/include/c++:${NATIVE_GCC}/include"
 
 case "$HOST" in
-    *darwin*)
-        export LIBRARY_PATH="${NATIVE_GCC}/lib"
-        ;;
+    *darwin*) export LIBRARY_PATH="${NATIVE_GCC}/lib" ;;
+    *mingw*) export LIBRARY_PATH="${NATIVE_GCC}/lib" ;;
     *)
         NATIVE_GCC_STATIC="$(store_path gcc-toolchain static)"
         export LIBRARY_PATH="${NATIVE_GCC}/lib:${NATIVE_GCC_STATIC}/lib"

contrib/guix/manifest.scm

@@ -517,7 +517,6 @@ inspecting signatures in Mach-O binaries.")
     (cond ((string-suffix? "-mingw32" target)
            (list ;; Native GCC 12 toolchain
                  gcc-toolchain-12
-                 (list gcc-toolchain-12 "static")
                  zip
                  (make-mingw-pthreads-cross-toolchain "x86_64-w64-mingw32")
                  nsis-x86_64