Fix NSS parallel build

This is just a minimal solution and obviously not fully parallel.
We still have to walk the tree twice:
1. copy all needed headers to dist (export export_private)
2. the parallel build (libs)

The fixes are:
* Add a few rm and @$(MAKE_OBJDIR) calls to various targets
* Serialize minimal steps in nss_build_all
  => Build libs of nss/lib and nss/cmd/lib before all other
  => drop the minimal all target
* Make $(SHARED_LIBRARY) depend on $(LIBRARY), otherwise dll lib
  creation on Windows builds a static lib, instead of the dll one
* Drop all "export:: private_export" rules. We run this before
  the build and duplicate targets break the header install

Change-Id: I1c35985c90d2d63990e04a0d2bb9d8ae921a2182
Reviewed-on: https://gerrit.libreoffice.org/62011
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

external/nss/ExternalProject_nss.mk

@@ -23,7 +23,7 @@ $(call gb_ExternalProject_get_state_target,nss,build): $(call gb_ExternalExecuta
 		$(if $(filter X86_64,$(CPUNAME)),USE_64=1) \
 		LIB="$(ILIB)" \
 		XCFLAGS="-arch:SSE $(SOLARINC)" \
-		$(MAKE) -j1 nss_build_all RC="rc.exe $(SOLARINC)" \
+		$(MAKE) nss_build_all RC="rc.exe $(SOLARINC)" \
 			NSINSTALL='$(call gb_ExternalExecutable_get_command,python) $(SRCDIR)/external/nss/nsinstall.py' \
 	,nss)
 
@@ -45,7 +45,7 @@ $(call gb_ExternalProject_get_state_target,nss,build): $(call gb_ExternalExecuta
 			$(if $(filter iOS-ARM,$(OS)-$(CPUNAME)),CPU_ARCH=arm) \
 			NSPR_CONFIGURE_OPTS="--build=$(BUILD_PLATFORM) --host=$(HOST_PLATFORM)") \
 		NSDISTMODE=copy \
-		$(MAKE) -j1 AR="$(AR)" \
+		$(MAKE) AR="$(AR)" \
 			RANLIB="$(RANLIB)" \
 			NMEDIT="$(NM)edit" \
 			COMMA=$(COMMA) \

external/nss/UnpackedTarball_nss.mk

@@ -34,6 +34,7 @@ $(eval $(call gb_UnpackedTarball_add_patches,nss,\
     	external/nss/nss.utf8bom.patch.1) \
 	$(if $(filter ANDROID,$(OS)), \
 		external/nss/nss-android.patch.1) \
+	external/nss/nss.parallel.patch \
 ))
 
 ifeq ($(COM_IS_CLANG),TRUE)