Calculate MPATH for sys/modules to save 92% time in a basic 'obj' tree-walk.

Sponsored by:	EMC / Isilon Storage Division

sys/conf/kmod.mk

@@ -370,8 +370,10 @@ vnode_if_typedef.h:
 .endif
 
 # Build _if.[ch] from _if.m, and clean them when we're done.
+# This is duplicated in sys/modules/Makefile.
 .if !defined(__MPATH)
 __MPATH!=find ${SYSDIR:tA}/ -name \*_if.m
+.export __MPATH
 .endif
 _MFILES=${__MPATH:T:O}
 _MPATH=${__MPATH:H:O:u}

sys/modules/Makefile

@@ -771,6 +771,12 @@ afterinstall:
 
 .include "${SYSDIR}/conf/config.mk"
 
+# Use sys/conf/kmod.mk's MPATH to avoid redundantly running in every subdir.
+.if !defined(__MPATH)
+__MPATH!=find ${SYSDIR:tA}/ -name \*_if.m
+.export __MPATH
+.endif
+
 SUBDIR:= ${SUBDIR:u:O}
 
 .include <bsd.subdir.mk>