RC: Pass output file in a way that llvm-rc 7 and below understand

Prior to LLVM 8.0, `llvm-rc` does not recognize `/fo` without a space
after it.  Add the space unconditionally because MS `rc` accepts it too.

Issue: #18957

Modules/CMakeRCInformation.cmake

@@ -32,7 +32,7 @@ set(CMAKE_INCLUDE_FLAG_RC "-I")
 # compile a Resource file into an object file
 if(NOT CMAKE_RC_COMPILE_OBJECT)
   set(CMAKE_RC_COMPILE_OBJECT
-    "<CMAKE_RC_COMPILER> <DEFINES> <INCLUDES> <FLAGS> /fo<OBJECT> <SOURCE>")
+    "<CMAKE_RC_COMPILER> <DEFINES> <INCLUDES> <FLAGS> /fo <OBJECT> <SOURCE>")
 endif()
 
 # set this variable so we can avoid loading this more than once.

Source/cmcldeps.cxx

@@ -276,7 +276,7 @@ int main()
 
     std::string clrest = rest;
     // rc: /fo x.dir\x.rc.res  ->  cl: /out:x.dir\x.rc.res.dep.obj
-    clrest = replace(clrest, "/fo", "/out:");
+    clrest = replace(clrest, "/fo ", "/out:");
     clrest = replace(clrest, objfile, objfile + ".dep.obj ");
 
     cl = "\"" + cl + "\" /P /DRC_INVOKED /TC ";

Source/cmcmd.cxx

@@ -1830,7 +1830,8 @@ int cmVSLink::LinkIncremental()
   // Compile the resource file.
   std::vector<std::string> rcCommand;
   rcCommand.push_back(this->RcPath.empty() ? "rc" : this->RcPath);
-  rcCommand.push_back("/fo" + this->ManifestFileRes);
+  rcCommand.emplace_back("/fo");
+  rcCommand.push_back(this->ManifestFileRes);
   rcCommand.push_back(this->ManifestFileRC);
   if (!RunCommand("RC Pass 1", rcCommand, this->Verbose, FORMAT_DECIMAL)) {
     return -1;