build: don't pass DESTCPU to configure unless set

If the DESTCPU wasn't manually set, the configure platform detection should be
better than the Makefile one. If it was manually set, add it to the
CONFIG_FLAGS.

As DESTCPU no longer needs to be manually set, just set ARCH.

Fixes: nodejs#13150

Makefile

@@ -34,6 +34,18 @@ ifdef DISABLE_V8_I18N
   V8_BUILD_OPTIONS += i18nsupport=off
 endif
 
+# Use Node arch names rather than V8 ones.
+ifeq ($(DESTCPU),ia32)
+  override DESTCPU=x86
+endif
+ifeq ($(DESTCPU),aarch64)
+  override DESTCPU=arm64
+endif
+
+ifdef DESTCPU
+  CONFIG_FLAGS += --dest-cpu=$(DESTCPU)
+endif
+
 BUILDTYPE_LOWER := $(shell echo $(BUILDTYPE) | tr '[A-Z]' '[a-z]')
 
 # Determine EXEEXT
@@ -564,86 +576,53 @@ RELEASE=$(shell sed -ne 's/\#define NODE_VERSION_IS_RELEASE \([01]\)/\1/p' src/n
 PLATFORM=$(shell uname | tr '[:upper:]' '[:lower:]')
 NPMVERSION=v$(shell cat deps/npm/package.json | grep '"version"' | sed 's/^[^:]*: "\([^"]*\)",.*/\1/')
 
-UNAME_M=$(shell uname -m)
-ifeq ($(findstring x86_64,$(UNAME_M)),x86_64)
-DESTCPU ?= x64
-else
-ifeq ($(findstring ppc64,$(UNAME_M)),ppc64)
-DESTCPU ?= ppc64
-else
-ifeq ($(findstring ppc,$(UNAME_M)),ppc)
-DESTCPU ?= ppc
-else
-ifeq ($(findstring s390x,$(UNAME_M)),s390x)
-DESTCPU ?= s390x
-else
-ifeq ($(findstring s390,$(UNAME_M)),s390)
-DESTCPU ?= s390
+ifdef DESTCPU
+  ARCH = $(DESTCPU)
 else
-ifeq ($(findstring arm,$(UNAME_M)),arm)
-DESTCPU ?= arm
-else
-ifeq ($(findstring aarch64,$(UNAME_M)),aarch64)
-DESTCPU ?= aarch64
-else
-ifeq ($(findstring powerpc,$(shell uname -p)),powerpc)
-DESTCPU ?= ppc64
-else
-DESTCPU ?= x86
-endif
-endif
-endif
-endif
-endif
-endif
-endif
-endif
-ifeq ($(DESTCPU),x64)
-ARCH=x64
-else
-ifeq ($(DESTCPU),arm)
-ARCH=arm
-else
-ifeq ($(DESTCPU),aarch64)
-ARCH=arm64
-else
-ifeq ($(DESTCPU),ppc64)
-ARCH=ppc64
-else
-ifeq ($(DESTCPU),ppc)
-ARCH=ppc
-else
-ifeq ($(DESTCPU),s390)
-ARCH=s390
-else
-ifeq ($(DESTCPU),s390x)
-ARCH=s390x
-else
-ARCH=x86
-endif
-endif
-endif
-endif
-endif
-endif
-endif
-
-# node and v8 use different arch names (e.g. node 'x86' vs v8 'ia32').
-# pass the proper v8 arch name to $V8_ARCH based on user-specified $DESTCPU.
-ifeq ($(DESTCPU),x86)
+  UNAME_M=$(shell uname -m)
+  ifeq ($(findstring x86_64,$(UNAME_M)),x86_64)
+    ARCH ?= x64
+  else
+  ifeq ($(findstring ppc64,$(UNAME_M)),ppc64)
+    ARCH ?= ppc64
+  else
+  ifeq ($(findstring ppc,$(UNAME_M)),ppc)
+    ARCH ?= ppc
+  else
+  ifeq ($(findstring s390x,$(UNAME_M)),s390x)
+    ARCH ?= s390x
+  else
+  ifeq ($(findstring s390,$(UNAME_M)),s390)
+    ARCH ?= s390
+  else
+  ifeq ($(findstring arm,$(UNAME_M)),arm)
+    ARCH ?= arm
+  else
+  ifeq ($(findstring aarch64,$(UNAME_M)),aarch64)
+    ARCH ?= aarch64
+  else
+  ifeq ($(findstring powerpc,$(shell uname -p)),powerpc)
+    ARCH ?= ppc64
+  else
+    ARCH ?= x86
+  endif
+  endif
+  endif
+  endif
+  endif
+  endif
+  endif
+  endif
+endif
+
+# Handle Node and V8 arch name differences for x86 and arm64.
+ifeq ($(ARCH),x86)
 V8_ARCH=ia32
-else
-V8_ARCH ?= $(DESTCPU)
-
 endif
-
-# enforce "x86" over "ia32" as the generally accepted way of referring to 32-bit intel
-ifeq ($(ARCH),ia32)
-override ARCH=x86
-endif
-ifeq ($(DESTCPU),ia32)
-override DESTCPU=x86
+ifeq ($(ARCH),arm64)
+V8_ARCH ?= aarch64
 endif
+V8_ARCH ?= $(ARCH)
 
 TARNAME=node-$(FULLVERSION)
 TARBALL=$(TARNAME).tar
@@ -762,7 +741,6 @@ doc-upload: doc
 $(TARBALL)-headers: release-only
 	$(PYTHON) ./configure \
 		--prefix=/ \
-		--dest-cpu=$(DESTCPU) \
 		--tag=$(TAG) \
 		--release-urlbase=$(RELEASE_URLBASE) \
 		$(CONFIG_FLAGS) $(BUILD_RELEASE_FLAGS)
@@ -794,7 +772,6 @@ $(BINARYTAR): release-only
 	$(RM) -r out/deps out/Release
 	$(PYTHON) ./configure \
 		--prefix=/ \
-		--dest-cpu=$(DESTCPU) \
 		--tag=$(TAG) \
 		--release-urlbase=$(RELEASE_URLBASE) \
 		$(CONFIG_FLAGS) $(BUILD_RELEASE_FLAGS)