Currently, there is nothing that prevents ONLY_FOR_ARCHS/NOT_FOR_ARCHS
from holding garbage.

The following patch adds a check, and promptly fixes an issue, namely
that ALL_ARCHES should also reference powerpc.

Index: arch-defines.mk
===================================================================
RCS file: /build/data/openbsd/cvs/ports/infrastructure/mk/arch-defines.mk,v
diff -u -p -r1.107 arch-defines.mk
--- arch-defines.mk	25 Jun 2024 13:48:24 -0000	1.107
+++ arch-defines.mk	26 Jul 2024 10:34:49 -0000
@@ -12,7 +12,7 @@
 ARCH ?!= uname -m
 
 ALL_ARCHS = aarch64 alpha amd64 arm arm64 armv7 hppa i386 landisk loongson \
-	luna88k m88k macppc mips64 mips64el octeon powerpc64 riscv64 sgi \
+	luna88k m88k macppc mips64 mips64el octeon powerpc powerpc64 riscv64 sgi \
 	sh sparc64
 # normally only list MACHINE_ARCH (uname -p) names in these variables,
 # but not all powerpc have apm(4), hence the use of macppc
Index: bsd.port.arch.mk
===================================================================
RCS file: /build/data/openbsd/cvs/ports/infrastructure/mk/bsd.port.arch.mk,v
diff -u -p -r1.14 bsd.port.arch.mk
--- bsd.port.arch.mk	16 Apr 2020 19:33:29 -0000	1.14
+++ bsd.port.arch.mk	26 Jul 2024 10:35:24 -0000
@@ -53,6 +53,11 @@ FLAVOR := ${FLAVOR:N$f}
 # build the actual list of subpackages we want
 BUILD_PACKAGES =
 
+# compute pattern for identifying bad variables
+.for A in ${ALL_ARCHS}
+_arch_check := ${_arch_check}:N${A}
+.endfor
+
 .for _s in ${MULTI_PACKAGES}
 
 # ONLY_FOR_ARCHS/NOT_FOR_ARCHS are special:
@@ -72,8 +77,13 @@ IGNORE${_s} += "Ignored as FLAVOR contai
 .    endif
 .  endfor
 
-# compute _ARCH_OK for ignore
 .  if defined(ONLY_FOR_ARCHS${_s})
+# validate against full architecture list
+.    for _m in ${_arch_check}
+.      if !empty(ONLY_FOR_ARCHS${_m})
+ERRORS += "Fatal: unrecognized architecture ${ONLY_FOR_ARCHS${_m}} in ONLY_FOR_ARCHS${_s}"
+.      endif
+.    endfor
 .    for A B in ${MACHINE_ARCH} ${ARCH}
 .      if empty(ONLY_FOR_ARCHS${_s}:M$A) && empty(ONLY_FOR_ARCHS${_s}:M$B)
 .        if ${MACHINE_ARCH} == "${ARCH}"
@@ -85,6 +95,12 @@ IGNORE${_s} += "is only for ${ONLY_FOR_A
 .    endfor
 .  endif
 .  if defined(NOT_FOR_ARCHS${_s})
+# validate against full architecture list
+.    for _m in ${_arch_check}
+.      if !empty(NOT_FOR_ARCHS${_m})
+ERRORS += "Fatal: unrecognized architecture ${NOT_FOR_ARCHS${_m}} in NOT_FOR_ARCHS${_s}"
+.      endif
+.    endfor
 .    for A B in ${MACHINE_ARCH} ${ARCH}
 .      if !empty(NOT_FOR_ARCHS${_s}:M$A) || !empty(NOT_FOR_ARCHS${_s}:M$B)
 IGNORE${_s} += "is not for ${NOT_FOR_ARCHS${_s}}"