llvm12: rework handling undefined options

Define a list of options and for any that aren't defined for the current
architecture add a PLIST_SUB entry as through the option were defined and
disabled.

devel/llvm12/Makefile

@@ -89,6 +89,8 @@ OPTIONS_DEFAULT_powerpc64le=     GOLD OPENMP
 OPTIONS_SINGLE=		BACKENDS
 OPTIONS_SINGLE_BACKENDS=BE_FREEBSD BE_NATIVE BE_STANDARD
 OPTIONS_SUB=	yes
+# All non-backend options
+_ALL_OPTIONS=	CLANG COMPILER_RT DOCS EXTRAS GOLD LIT LLD LLDB PYCLANG OPENMP
 
 BE_AMDGPU_DESC=		AMD GPU backend (required by mesa)
 BE_FREEBSD_DESC=	Backends for FreeBSD architectures
@@ -436,23 +438,12 @@ CONFIGURE_ENV+=	COMPILER_PATH=${LOCALBASE}/bin
 MAKE_ENV+=	COMPILER_PATH=${LOCALBASE}/bin
 .endif
 
-.if ! ${OPTIONS_DEFINE:MCOMPILER_RT}
-# Hack to disable COMPILER_RT in plist of unsupported architectures
-PLIST_SUB+=	COMPILER_RT="@comment "
-.else
-.endif
-
-.if ! ${OPTIONS_DEFINE:MGOLD}
-# Hack to disable GOLD in plist of unsupported architectures
-PLIST_SUB+=	GOLD="@comment "
-.else
-.endif
-
-.if ! ${OPTIONS_DEFINE:MOPENMP}
-# Hack to disable OPENMP in plist of unsupported architectures
-PLIST_SUB+=	OPENMP="@comment "
-.else
+# Comment out plist entries for unsupported options.
+.for opt in ${_ALL_OPTIONS}
+.if !${OPTIONS_DEFINE:M${opt}}
+PLIST_SUB+=     ${opt}="@comment "
 .endif
+.endfor
 
 post-patch:
 	${REINPLACE_CMD} -e 's|import lit|import lit${LLVM_SUFFIX}|' \