Bootstrap libz when cross-building from non-FreeBSD

This is needed now libdwarf depends on libz.

Fixes:		dbf05458e3 ("libdwarf: Support consumption of compressed ELF sections")
MFC after:	1 week

Makefile.inc1

@@ -2469,6 +2469,10 @@ _other_bootstrap_tools+=usr.bin/bmake
 # Avoid dependency on host bz2 headers:
 _other_bootstrap_tools+=lib/libbz2
 ${_bt}-usr.bin/grep: ${_bt}-lib/libbz2
+
+# libdwarf depends on libz
+_other_bootstrap_tools+=lib/libz
+${_bt}-lib/libdwarf: ${_bt}-lib/libz
 .else
 # All tools in _basic_bootstrap_tools have the same name as the subdirectory
 # so we can use :T to get the name of the symlinks that we need to create.

lib/libz/Makefile

@@ -38,9 +38,14 @@ SRCS+=		inflate.c
 SRCS+=		inftrees.c
 SRCS+=		trees.c
 SRCS+=		uncompr.c
-SRCS+=		zopen.c
 SRCS+=		zutil.c
 
+# Wrapper relies on FreeBSD-specific fpos_t representation and non-portable
+# funopen. Not needed for bootstrapping, so just disable it.
+.if ${.MAKE.OS} == "FreeBSD" || !defined(BOOTSTRAPPING)
+SRCS+=		zopen.c
+.endif
+
 .if ${MACHINE_ARCH} == "i386" || ${MACHINE_ARCH} == "amd64"
 CFLAGS+=	-DUNALIGNED_OK
 .endif

tools/build/mk/Makefile.boot

@@ -16,7 +16,6 @@ NM:=	/usr/bin/nm
 
 # Avoid stale dependecy warnings:
 LIBC:=
-LIBZ:=
 LIBM:=
 LIBUTIL:=
 LIBCPLUSPLUS:=
@@ -30,6 +29,7 @@ LIBL:=${WORLDTMP}/legacy/usr/lib/libl.a
 LIBROKEN:=${WORLDTMP}/legacy/usr/lib/libroken.a
 LIBDWARF:=${WORLDTMP}/legacy/usr/lib/libdwarf.a
 LIBELF:=${WORLDTMP}/legacy/usr/lib/libelf.a
+LIBZ:=${WORLDTMP}/legacy/usr/lib/libz.a
 
 # Add various -Werror flags to catch missing function declarations
 CFLAGS+=	-Werror=implicit-function-declaration -Werror=implicit-int \