Fix make bootstrapping with WITH_DEBUG_FILES=

A HEAD buildworld on 9.x first bootstraps bmake, but this failed when
building with standalone debug.  Pass in the PROGNAME override to the
'make all' stage as well as 'make install' so that the .debug file is
created with the correct name.

Reviewed by:	sjg
Sponsored by:	The FreeBSD Foundation
Approved by:	re (rodrigc)

Makefile

@@ -351,7 +351,7 @@ make bmake: .PHONY
 	${_+_}@cd ${.CURDIR}/usr.bin/${.TARGET}; \
 		${MMAKE} obj DESTDIR= && \
 		${MMAKE} depend DESTDIR= && \
-		${MMAKE} all DESTDIR= && \
+		${MMAKE} all DESTDIR= PROGNAME=${MYMAKE:T} && \
 		${MMAKE} install DESTDIR=${MYMAKE:H} BINDIR= PROGNAME=${MYMAKE:T}
 
 tinderbox toolchains kernel-toolchains: upgrade_checks