Makefile.libcompat: Handle MK_FOO varying for native and compat arches

Currently Makefile.libcompat queries a few MK_FOO variables to determine
what is being built. However, it is plausible (and indeed, downstream
in CheriBSD, this is the case) that these may vary between the native
and the compat architecture. In order to correctly determine their
values for the compat architecture, we need to defer their evaluation
until we are in the compat sub-make where src.opts.mk will give us the
right value for the compat MACHINE_ARCH.

Reviewed by:	brooks, jhb, imp
Obtained from:	CheriBSD
Differential Revision:	https://reviews.freebsd.org/D40570

Makefile.libcompat

@@ -39,6 +39,46 @@ LIBCOMPATIMAKE+=	${LIBCOMPATWMAKE:NINSTALL=*:NDESTDIR=*} \
 			MK_INCLUDES=no \
 			-DLIBRARIES_ONLY
 
+# Shared logic
+build${libcompat}: .PHONY
+	@echo
+	@echo "--------------------------------------------------------------"
+	@echo ">>> stage 4.3: building lib${libcompat} shim libraries"
+	@echo "--------------------------------------------------------------"
+	${WORLDTMP_MTREE} -f ${.CURDIR}/etc/mtree/BSD.lib${libcompat}.dist \
+	    -p ${WORLDTMP}/usr >/dev/null
+.if ${MK_DEBUG_FILES} != "no"
+	${WORLDTMP_MTREE} -f ${.CURDIR}/etc/mtree/BSD.lib${libcompat}.dist \
+	    -p ${WORLDTMP}/usr/lib/debug/usr >/dev/null
+.endif
+	${_+_}cd ${.CURDIR}; \
+	    WORLDTMP=${WORLDTMP} \
+	    MAKEFLAGS="-m ${.CURDIR}/tools/build/mk ${.MAKEFLAGS}" \
+	    ${MAKE} -f Makefile.inc1 \
+	    DESTDIR= \
+	    OBJTOP=${LIBCOMPAT_OBJTOP} \
+	    OBJROOT='$${OBJTOP}/' \
+	    MAKEOBJDIRPREFIX= \
+	    -DNO_LINT \
+	    -DNO_CPU_CFLAGS \
+	    MK_ASAN=no \
+	    MK_CTF=no \
+	    MK_RETPOLINE=no \
+	    MK_SSP=no \
+	    MK_UBSAN=no \
+	    MK_WERROR=no \
+	    _lc_build-tools
+	${_+_}cd ${.CURDIR}; \
+	    ${LIBCOMPATWMAKE} -f Makefile.inc1 -DNO_FSCHG libraries
+
+distribute${libcompat} install${libcompat}: .PHONY
+	${_+_}cd ${.CURDIR}; \
+	    ${LIBCOMPATIMAKE} -f Makefile.inc1 _lc_${.TARGET:S/${libcompat}$//}
+
+# These depend on MK_*, which could vary between the native and compat
+# architectures. Thus targets using them are run within a compat sub-make
+# rather than the native make environment.
+
 _LC_LIBDIRS.yes=		lib
 _LC_LIBDIRS.yes+=		gnu/lib
 _LC_LIBDIRS.${MK_CDDL:tl}+=	cddl/lib
@@ -52,46 +92,16 @@ _libmagic=	lib/libmagic
 _jevents=	lib/libpmc/pmu-events
 .endif
 
-
-# Shared logic
-build${libcompat}: .PHONY
-	@echo
-	@echo "--------------------------------------------------------------"
-	@echo ">>> stage 4.3: building lib${libcompat} shim libraries"
-	@echo "--------------------------------------------------------------"
-	${WORLDTMP_MTREE} -f ${.CURDIR}/etc/mtree/BSD.lib${libcompat}.dist \
-	    -p ${WORLDTMP}/usr >/dev/null
-.if ${MK_DEBUG_FILES} != "no"
-	${WORLDTMP_MTREE} -f ${.CURDIR}/etc/mtree/BSD.lib${libcompat}.dist \
-	    -p ${WORLDTMP}/usr/lib/debug/usr >/dev/null
-.endif
+_lc_build-tools:
 .for _dir in lib/ncurses/tinfo ${_libmagic} ${_jevents}
 .for _t in ${_obj} build-tools
-	${_+_}cd ${.CURDIR}/${_dir}; \
-	    WORLDTMP=${WORLDTMP} \
-	    MAKEFLAGS="-m ${.CURDIR}/tools/build/mk ${.MAKEFLAGS}" \
-	    ${MAKE} DESTDIR= \
-	    OBJTOP=${LIBCOMPAT_OBJTOP} \
-	    OBJROOT='$${OBJTOP}/' \
-	    MAKEOBJDIRPREFIX= \
-	    DIRPRFX=${_dir}/ \
-	    -DNO_LINT \
-	    -DNO_CPU_CFLAGS \
-	    MK_ASAN=no \
-	    MK_CTF=no \
-	    MK_RETPOLINE=no \
-	    MK_SSP=no \
-	    MK_UBSAN=no \
-	    MK_WERROR=no \
-	    ${_t}
+	${_+_}cd ${.CURDIR}/${_dir}; ${MAKE} DIRPRFX=${_dir}/ ${_t}
 .endfor
 .endfor
-	${_+_}cd ${.CURDIR}; \
-	    ${LIBCOMPATWMAKE} -f Makefile.inc1 -DNO_FSCHG libraries
 
-distribute${libcompat} install${libcompat}: .PHONY
+_lc_distribute _lc_install:
 .for _dir in ${_LC_LIBDIRS.yes}
-	${_+_}cd ${.CURDIR}/${_dir}; ${LIBCOMPATIMAKE} ${.TARGET:S/${libcompat}$//}
+	${_+_}cd ${.CURDIR}/${_dir}; ${MAKE} ${.TARGET:S/^_lc_//}
 .endfor
 
 .endif # !targets(__<${_this:T}>__)