Choose the correct startup object for mingw-w64

If -municode is passed to mingw-w64's gcc, then crt2u.o (which causes
wmain to be selected) should be linked rather than crt2.o. In passing,
the code now sniffs for -nostartfiles, which causes neither crt2.o nor
crt2u.o to be considered.

Author: dra27

CHANGES

@@ -1,7 +1,8 @@
 Next version
 - GPR#127: Recognise hyphens in option names in the COFF .drectve section. Fixes #126 (Reza Barazesh)
 - GPR#136: Fix parallel access crashes and misbehavior (David Allsopp, Jan Midtgaard, Antonin Décimo)
-
+- GPR#146: For mingw-w64, select crt2u.o instead of crt2.o if -link -municode
+  is specified (David Allsopp)
 
 Version 0.43
 - GPR#108: Add -lgcc_s to Cygwin's link libraries, upstreaming a patch from the

reloc.ml

@@ -1378,8 +1378,14 @@ let setup_toolchain () =
     default_libs :=
       ["-lmingw32"; "-lgcc"; "-lgcc_eh"; "-lmoldname"; "-lmingwex"; "-lmsvcrt";
        "-luser32"; "-lkernel32"; "-ladvapi32"; "-lshell32" ];
-    if !exe_mode = `EXE then default_libs := "crt2.o" :: !default_libs
-    else default_libs := "dllcrt2.o" :: !default_libs
+    if not (List.mem "-nostartfiles" !extra_args) then begin
+      if !exe_mode = `EXE then
+        if List.mem "-municode" !extra_args then
+          default_libs := "crt2u.o" :: !default_libs
+        else
+          default_libs := "crt2.o" :: !default_libs
+      else default_libs := "dllcrt2.o" :: !default_libs
+    end
   in
   match !toolchain with
   | _ when !builtin_linker ->