ICU-20782 Add support for cross-compiling Windows ARM/ARM64 data DLL from the x64 bits.

icu4c/source/data/makedata.mak

@@ -71,6 +71,7 @@ ICUSRCDATA_RELATIVE_PATH=..\..\..
 # Timestamp files to keep track of current build state
 TOOLS_TS=$(ICUTMP)\tools.timestamp
 COREDATA_TS=$(ICUTMP)\coredata.timestamp
+ARM_CROSSBUILD_TS=
 
 #  ICUCOL
 #       The directory that contains colfiles.mk files along with *.txt collation data files
@@ -115,6 +116,7 @@ DLL_OUTPUT=$(ICUP)\bin32$(UWP)
 !ELSE
 DLL_OUTPUT=$(ICUP)\bin$(UWP)
 !ENDIF
+!MESSAGE ICU data DLL_OUTPUT path is $(DLL_OUTPUT)
 
 #
 #  TESTDATA
@@ -140,19 +142,37 @@ TESTDATABLD=$(ICUP)\source\test\testdata\out\build
 ICUTOOLS=$(ICUP)\source\tools
 !MESSAGE ICU tools path is $(ICUTOOLS)
 
+#   ARM_CROSS_BUILD
+#       In order to support cross-compiling for ARM/ARM64 using the x64 tools
+#       we need to know if we're building the ARM/ARM64 data DLL, otherwise
+#       the existence of the x64 bits will cause us to think we are already done.
+#    Note: This is only for the "regular" builds, the UWP builds have a separate project file entirely.
+ARM_CROSS_BUILD=
+!IF "$(UWP)" == ""
+!IF "$(CFG)" == "ARM\Release" || "$(CFG)" == "ARM\Debug"
+ARM_CROSS_BUILD=ARM
+ARM_CROSSBUILD_TS=$(ICUTMP)\$(ARM_CROSS_BUILD).timestamp
+!ELSE IF "$(CFG)" == "ARM64\Release"  || "$(CFG)" == "ARM64\Debug"
+ARM_CROSS_BUILD=ARM64
+ARM_CROSSBUILD_TS=$(ICUTMP)\$(ARM_CROSS_BUILD).timestamp
+!ENDIF
+!ENDIF
+
 #
 #  TOOLS CFG PATH
-#      Generally the tools want to run on the same architechure as is being built.
+#      Generally the tools want to run on the same architecture as is being built.
 #      Thus ARM and ARM64 need to use another build of the other tools, so make sure to get an usable cfg path.
 #      Since tools, particularly pkggen, have architecture built-in, we made x64 on
 #      Windows be machine-independent and use those tools.
 #
+!IF "$(ARM_CROSS_BUILD)" == ""
 CFGTOOLS=$(CFG)
-!IF "$(CFG)" == "ARM\Release" || "$(CFG)" == "ARM\Debug" || "$(CFG)" == "ARM64\Release"  || "$(CFG)" == "ARM64\Debug"
+!ELSE
 CFGTOOLS=x64\Release
 !ENDIF
 !MESSAGE ICU tools CFG subpath is $(CFGTOOLS)
 
+
 # The current ICU tools need to be in the path first.
 # x86 uses x86; x64, arm, and arm64 use x64
 !IF "$(CFG)" == "x86\Release" || "$(CFG)" == "x86\Debug"
@@ -210,6 +230,7 @@ COMMON_ICUDATA_ARGUMENTS=$(COMMON_ICUDATA_ARGUMENTS) -a ARM64
 #				Building the common dll in $(ICUBLD_PKG) unconditionally copies it to $(DLL_OUTPUT) too.
 #
 #############################################################################
+!IF "$(ARM_CROSS_BUILD)" == ""
 ALL : GODATA "$(ICU_LIB_TARGET)" "$(TESTDATAOUT)\testdata.dat"
 	@echo All targets are up to date
 
@@ -218,6 +239,11 @@ ALL : GODATA "$(ICU_LIB_TARGET)" "$(TESTDATAOUT)\testdata.dat"
     copy "$(ICUOUT)\$(U_ICUDATA_NAME)$(U_ICUDATA_ENDIAN_SUFFIX).dat" "$(ICUMAKE)\..\..\commondata\"
 !ENDIF
 
+!ELSE
+ALL : GODATA "$(ICU_LIB_TARGET)" "$(TESTDATAOUT)\testdata.dat" $(ARM_CROSSBUILD_TS)
+	@echo All targets are up to date
+
+!ENDIF
 
 # Three main targets: tools, core data, and test data.
 # Keep track of whether they are built via timestamp files.
@@ -385,6 +411,18 @@ icu4j-data-install :
 	-@erase "$(ICUTMP)\$(ICUPKG).dat"
 !ENDIF
 
+"$(ARM_CROSSBUILD_TS)" : $(COMMON_ICUDATA_DEPENDENCIES) "$(ICU_LIB_TARGET)"
+    @echo Building ICU data for "$(ARM_CROSS_BUILD)" from x64
+	cd "$(ICUBLD_PKG)"
+	"$(ICUPBIN)\pkgdata" $(COMMON_ICUDATA_ARGUMENTS) $(ICUTMP)\icudata.lst
+	-@erase "$(ICU_LIB_TARGET)"
+	@if not exist "$(DLL_OUTPUT)" mkdir "$(DLL_OUTPUT)"
+	copy "$(U_ICUDATA_NAME).dll" "$(ICU_LIB_TARGET)"
+	-@erase "$(U_ICUDATA_NAME).dll"
+	copy "$(ICUTMP)\$(ICUPKG).dat" "$(ICUOUT)\$(U_ICUDATA_NAME)$(U_ICUDATA_ENDIAN_SUFFIX).dat"
+	-@erase "$(ICUTMP)\$(ICUPKG).dat"
+    @echo "timestamp" > $(ARM_CROSSBUILD_TS)
+
 # utility target to create missing directories
 # Most directories are made by Python, but still create ICUTMP
 # so it works in the source archive