Build changes for XCode 13

Weave builds for iOS have been arguably somewhat incorrect.  The
Makefile-iOS used to generate a single Weave.framework for both
iPhoneOS and for iPhoneSimulator.  This became problematic in XCode
13, when the simulator architectures (x86_64, i386) were no longer
supported in the iPhoneOS set of libraries, and builds have
consequently started to fail.

This patch passes different sysroots to the linker depending on
whether the target is a iPhoneOS or an iPhoneSimulator.

Bug: 190421934
Test: build succeeded on local machine, awaiting confirmation from maloo@
Change-Id: Ib3d2207d77388c00e8c1e397f6dd13fda1cb4d26

Makefile-iOS

@@ -111,7 +111,9 @@ AbsTopResultDir                                                 = $(PWD)/$(TopRe
 TargetTupleStem                                         = apple-darwin
 TargetTuple                                             = $(TargetTupleStem)-ios
 
-ARCHS                                                   = arm64 armv7 armv7s i386 x86_64
+DEVICE_ARCHS                                            = arm64 armv7 armv7s
+SIMULATOR_ARCHS                                         = i386 x86_64
+ARCHS                                                   = $(DEVICE_ARCHS) $(SIMULATOR_ARCHS)
 
 TopTargetLibDir                                         = $(TopResultDir)/$(if $(1),$(1)-,)$(TargetTuple)/lib
 
@@ -138,11 +140,14 @@ FrameworkPlist                                          = $(Framework)/$(Framewo
 FrameworkModuleMap                                      = $(Framework)/$(FrameworkModulesDirName)/$(FrameworkModuleMapName)
 
 FRAMEWORK_ARCHFLAGS                                     = $(addprefix -arch ,$(ARCHS))
+DEVICE_XARCHS                                           = $(foreach arch, $(DEVICE_ARCHS),-Xarch_$(arch) -isysroot$(IOS_DEVICE_SDK))
+SIMULATOR_XARCHS                                        = $(foreach arch, $(SIMULATOR_ARCHS),-Xarch_$(arch) -isysroot$(IOS_SIMULATOR_SDK))
 FRAMEWORK_FLAGS                                         = \
         $(FRAMEWORK_ARCHFLAGS) \
         $(IOS_MIN_VERSION_FLAG) \
         $(FRAMEWORK_ARCHFLAGS) \
-        -isysroot $(IOS_DEVICE_SDK) \
+	$(DEVICE_XARCHS) \
+	$(SIMULATOR_XARCHS) \
         -I$(IOS_DEVICE_SDK)/$(CoreFoundationHeaders) \
         -fpic \
         -lc++ \