Define all other architectures as "not x86"

This allows the build to proceed for AArch64 (mentioned in #10791) and others.

(cherry picked from commit f244fb6)
ref #13558

Make.inc

@@ -525,14 +525,9 @@ ISX86=1
 else ifeq ($(ARCH),x86_64)
 BINARY=64
 ISX86=1
-else ifneq (,$(findstring arm,$(ARCH)))
-ISX86=0
-else ifneq (,$(findstring powerpc,$(ARCH)))
-ISX86=0
-else ifneq (,$(findstring ppc,$(ARCH)))
-ISX86=0
 else
-$(error "unknown word-size for arch: $(ARCH)")
+# For all other architectures (ARM, PPC, AArch64, etc.)
+ISX86=0
 endif
 
 # If we are running on ARM, set certain options automatically