Inconsistent installation path for libsepol.so breaks DESTDIR-based cross-compilation

[Sdup1dXXY]

Hi SELinux maintainers,

While cross-compiling libsepol for an embedded target, I noticed an inconsistency in the installation paths defined in the top-level Makefile:

• Static library (libsepol.a) and .pc file are installed to:
  $(DESTDIR)$(LIBDIR) → typically /usr/lib under PREFIX
• Shared library (libsepol.so.X.Y) is installed to:
  $(DESTDIR)$(SHLIBDIR) → hardcoded as /lib, outside of PREFIX

This causes the actual .so file to be installed into my host system’s /lib, rather than under the intended staging directory ($(PREFIX)/lib), which breaks packaging and pollutes the host system during cross-compilation.

Here's the Makefile in the src directory of the libsepol source:

PREFIX ?= /usr
INCLUDEDIR ?= $(PREFIX)/include
LIBDIR ?= $(PREFIX)/lib
SHLIBDIR ?= /lib
RANLIB ?= ranlib
CILDIR ?= ../cil

......

install: all
        test -d $(DESTDIR)$(LIBDIR) || install -m 755 -d $(DESTDIR)$(LIBDIR)
        install -m 644 $(LIBA) $(DESTDIR)$(LIBDIR)
        test -d $(DESTDIR)$(LIBDIR)/pkgconfig || install -m 755 -d $(DESTDIR)$(LIBDIR)/pkgconfig
        install -m 644 $(LIBPC) $(DESTDIR)$(LIBDIR)/pkgconfig
ifneq ($(DISABLE_SHARED),y)
        test -d $(DESTDIR)$(SHLIBDIR) || install -m 755 -d $(DESTDIR)$(SHLIBDIR)
        install -m 755 $(LIBSO) $(DESTDIR)$(SHLIBDIR)
        $(LN) -sf --relative $(DESTDIR)$(SHLIBDIR)/$(LIBSO) $(DESTDIR)$(LIBDIR)/$(TARGET)
endif