depends: always use correct ar for win qt

fanquake · fanquake · commit 300918075144 · 2022-07-26T09:38:42.000+01:00
If we don't set this explicitly, then qt will still use it's default
windows ar, when building with LTO (when we want it to use gcc-ar).

So set `QMAKE_LIB` which is used for win32, and defaults to `ar -rc`.
This way we always get the correct ar.

Issue can be seen building in Guix with LTO. i.e:
```bash
x86_64-w64-mingw32-ar: .obj/release/hb-blob.o: plugin needed to handle lto object
```
diff --git a/depends/packages/qt.mk b/depends/packages/qt.mk
@@ -177,6 +177,7 @@ $(package)_config_opts_mingw32 += "QMAKE_CFLAGS = '$($(package)_cflags) $($(pack
 $(package)_config_opts_mingw32 += "QMAKE_CXX = '$($(package)_cxx)'"
 $(package)_config_opts_mingw32 += "QMAKE_CXXFLAGS = '$($(package)_cxxflags) $($(package)_cppflags)'"
 $(package)_config_opts_mingw32 += "QMAKE_LFLAGS = '$($(package)_ldflags)'"
+$(package)_config_opts_mingw32 += "QMAKE_LIB = '$($(package)_ar) rc'"
 $(package)_config_opts_mingw32 += -device-option CROSS_COMPILE="$(host)-"
 $(package)_config_opts_mingw32 += -pch
 
