8571 Makefile.master should not trust $PATH

@@ -132,13 +132,20 @@
 STABS=          $(ONBLD_TOOLS)/bin/$(MACH)/stabs
 ELFEXTRACT=     $(ONBLD_TOOLS)/bin/$(MACH)/elfextract
 MBH_PATCH=      $(ONBLD_TOOLS)/bin/$(MACH)/mbh_patch
 BTXLD=          $(ONBLD_TOOLS)/bin/$(MACH)/btxld
 VTFONTCVT=      $(ONBLD_TOOLS)/bin/$(MACH)/vtfontcvt
+# echo(1) and true(1) are specified without absolute paths, so that the shell
+# spawned by make(1) may use the built-in versions.  This is minimally
+# problematic, as the shell spawned by make(1) is known and under control, the
+# only risk being if the shell falls back to $PATH.
+#
+# We specifically want an echo(1) that does interpolation of escape sequences,
+# which ksh93, /bin/sh, and bash will all provide.
 ECHO=           echo
-INS=            install
 TRUE=           true
+INS=            $(ONBLD_TOOLS)/bin/$(MACH)/install
 SYMLINK=        /usr/bin/ln -s
 LN=             /usr/bin/ln
 CHMOD=          /usr/bin/chmod
 MV=             /usr/bin/mv -f
 RM=             /usr/bin/rm -f