gnu: cmake: Fix cross-compilation.

* gnu/packages/cmake.scm (cmake-minimal-cross): New package.
* guix/build-system/cmake.scm (default-cmake): Add new target argument and use
it to select cmake-minimal or cmake-minimal-cross.
(lower): Pass target to default-cmake.

gnu/packages/cmake.scm

@@ -219,6 +219,14 @@ (define-public cmake/fixed
                (append (search-patches "cmake-curl-certificates.patch")
                        (origin-patches (package-source cmake))))))))
 
+(define-public cmake-minimal-cross
+  (package
+    (inherit cmake-minimal)
+    (name "cmake-minimal-cross")
+    (native-search-paths '())
+    (search-paths
+     (package-native-search-paths cmake-minimal))))
+
 (define-public emacs-cmake-mode
   (package
     (inherit cmake)

guix/build-system/cmake.scm

@@ -43,16 +43,19 @@ (define %cmake-build-system-modules
   `((guix build cmake-build-system)
     ,@%gnu-build-system-modules))
 
-(define (default-cmake)
+(define (default-cmake target)
   "Return the default CMake package."
 
   ;; Do not use `@' to avoid introducing circular dependencies.
   (let ((module (resolve-interface '(gnu packages cmake))))
-    (module-ref module 'cmake-minimal)))
+    (module-ref module
+                (if target
+                    'cmake-minimal-cross
+                    'cmake-minimal))))
 
 (define* (lower name
                 #:key source inputs native-inputs outputs system target
-                (cmake (default-cmake))
+                (cmake (default-cmake target))
                 #:allow-other-keys
                 #:rest arguments)
   "Return a bag for NAME."