Honor $(STRIP) in install-strip for cross-compilation (#1024)

* Honor $(STRIP) in install-strip for cross-compilation

The install-strip target hard-coded `install -s`, which strips via the
install program using the build host's strip and ignores the STRIP
variable. When cross-compiling this runs the host strip against a
target binary and fails.

Pass --strip-program=$(or $(STRIP),strip) so the target strip is used
when STRIP is set (as cross toolchains and build systems provide),
falling back to plain `strip` for native builds. A plain `make install`
is unaffected.

* Make install-strip portable (address review)

- Detect the target strip via AC_CHECK_TOOL([STRIP],[strip],[strip]) in
  configure.ac (picks up the cross-prefixed strip when cross-compiling,
  defaults to plain strip otherwise) and substitute @STRIP@ in Makefile.in.
- Rewrite install-strip to run a normal install then $(STRIP) on the
  installed rsync binary, dropping the GNU Make $(or ...) and the GNU
  install --strip-program extension that broke with install-sh/BSD install.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Makefile.in

@@ -21,6 +21,7 @@ LIBOBJDIR=lib/
 
 INSTALLCMD=@INSTALL@
 INSTALLMAN=@INSTALL@
+STRIP=@STRIP@
 
 srcdir=@srcdir@
 MKDIR_P=@MKDIR_P@
@@ -116,7 +117,8 @@ install-ssl-daemon: stunnel-rsyncd.conf
 install-all: install install-ssl-daemon
 
 install-strip:
-	$(MAKE) INSTALL_STRIP='-s' install
+	$(MAKE) install
+	$(STRIP) $(DESTDIR)$(bindir)/rsync$(EXEEXT)
 
 .PHONY: uninstall
 uninstall:

configure.ac

@@ -59,6 +59,7 @@ AC_PROG_CXX
 AC_PROG_AWK
 AC_PROG_EGREP
 AC_PROG_INSTALL
+AC_CHECK_TOOL([STRIP], [strip], [strip])
 AC_PROG_MKDIR_P
 AC_SUBST(SHELL)
 AC_PATH_PROG([PERL], [perl])