libsepol: build: follow standard semantics for DESTDIR and PREFIX

This patch solves the following issues:
- The pkg-config files generates odd paths when using DESTDIR without PREFIX
- DESTDIR is needed during compile time to compute library and header paths which it should not.
- Installing with both DESTDIR and PREFIX set gives us odd paths
- Make usage of DESTDIR and PREFIX more standard

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>

diff -durN libsepol.orig/include/Makefile libsepol/include/Makefile
--- libsepol.orig/include/Makefile	2018-01-12 12:42:30.908709792 +0100
+++ libsepol/include/Makefile	2018-01-12 09:58:04.322148228 +0100
@@ -1,6 +1,6 @@
 # Installation directories.
-PREFIX ?= $(DESTDIR)/usr
-INCDIR ?= $(PREFIX)/include/sepol
+PREFIX ?= /usr
+INCDIR = $(DESTDIR)$(PREFIX)/include/sepol
 CILDIR ?= ../cil
 
 all:
diff -durN libsepol.orig/man/Makefile libsepol/man/Makefile
--- libsepol.orig/man/Makefile	2018-01-12 12:42:30.912043126 +0100
+++ libsepol/man/Makefile	2018-01-12 09:58:04.322148228 +0100
@@ -1,6 +1,7 @@
 # Installation directories.
-MAN8DIR ?= $(DESTDIR)/usr/share/man/man8
-MAN3DIR ?= $(DESTDIR)/usr/share/man/man3
+PREFIX ?= /usr
+MAN8DIR ?= $(DESTDIR)$(PREFIX)/share/man/man8
+MAN3DIR ?= $(DESTDIR)$(PREFIX)/share/man/man3
 
 all:
 
diff -durN libsepol.orig/src/libsepol.pc.in libsepol/src/libsepol.pc.in
--- libsepol.orig/src/libsepol.pc.in	2018-01-12 12:42:30.912043126 +0100
+++ libsepol/src/libsepol.pc.in	2018-01-12 09:58:04.322148228 +0100
@@ -1,6 +1,6 @@
 prefix=@prefix@
 exec_prefix=${prefix}
-libdir=${exec_prefix}/@libdir@
+libdir=@libdir@
 includedir=@includedir@
 
 Name: libsepol
diff -durN libsepol.orig/src/Makefile libsepol/src/Makefile
--- libsepol.orig/src/Makefile	2018-01-12 12:42:30.912043126 +0100
+++ libsepol/src/Makefile	2018-01-12 09:58:04.322148228 +0100
@@ -1,11 +1,10 @@
 # Installation directories.
-PREFIX ?= $(DESTDIR)/usr
+PREFIX ?= /usr
 INCLUDEDIR ?= $(PREFIX)/include
 LIBDIR ?= $(PREFIX)/lib
-SHLIBDIR ?= $(DESTDIR)/lib
 RANLIB ?= ranlib
-LIBBASE ?= $(shell basename $(LIBDIR))
 CILDIR ?= ../cil
+LIBINSTALL = $(DESTDIR)$(LIBDIR)
 
 VERSION = $(shell cat ../VERSION)
 LIBVERSION = 1
@@ -52,7 +51,7 @@
 	ln -sf $@ $(TARGET) 
 
 $(LIBPC): $(LIBPC).in ../VERSION
-	sed -e 's/@VERSION@/$(VERSION)/; s:@prefix@:$(PREFIX):; s:@libdir@:$(LIBBASE):; s:@includedir@:$(INCLUDEDIR):' < $< > $@
+	sed -e 's/@VERSION@/$(VERSION)/; s:@prefix@:$(PREFIX):; s:@libdir@:$(LIBDIR):; s:@includedir@:$(INCLUDEDIR):' < $< > $@
 
 $(LIBMAP): $(LIBMAP).in
 ifneq ($(DISABLE_CIL),y)
@@ -80,16 +79,16 @@
 	$(CC) $(CFLAGS) -fPIC -DSHARED -c -o $@ $<
 
 install: all
-	test -d $(LIBDIR) || install -m 755 -d $(LIBDIR)
-	install -m 644 $(LIBA) $(LIBDIR)
-	test -d $(SHLIBDIR) || install -m 755 -d $(SHLIBDIR)
-	install -m 755 $(LIBSO) $(SHLIBDIR)
-	test -d $(LIBDIR)/pkgconfig || install -m 755 -d $(LIBDIR)/pkgconfig
-	install -m 644 $(LIBPC) $(LIBDIR)/pkgconfig
-	$(LN) -sf --relative $(SHLIBDIR)/$(LIBSO) $(LIBDIR)/$(TARGET)
+	test -d $(LIBINSTALL) || install -m 755 -d $(LIBINSTALL)
+	install -m 644 $(LIBA) $(LIBINSTALL)
+	test -d $(LIBINSTALL) || install -m 755 -d $(LIBINSTALL)
+	install -m 755 $(LIBSO) $(LIBINSTALL)
+	test -d $(LIBINSTALL)/pkgconfig || install -m 755 -d $(LIBINSTALL)/pkgconfig
+	install -m 644 $(LIBPC) $(LIBINSTALL)/pkgconfig
+	$(LN) -sf --relative $(LIBINSTALL)/$(LIBSO) $(LIBINSTALL)/$(TARGET)
 
 relabel:
-	/sbin/restorecon $(SHLIBDIR)/$(LIBSO)
+	/sbin/restorecon $(LIBINSTALL)/$(LIBSO)
 
 clean: 
 	-rm -f $(LIBPC) $(LIBMAP) $(OBJS) $(LOBJS) $(LIBA) $(LIBSO) $(TARGET) $(CIL_GENERATED)
diff -durN libsepol.orig/utils/Makefile libsepol/utils/Makefile
--- libsepol.orig/utils/Makefile	2018-01-12 12:42:30.915376458 +0100
+++ libsepol/utils/Makefile	2018-01-12 09:58:04.322148228 +0100
@@ -1,6 +1,6 @@
 # Installation directories.
-PREFIX ?= $(DESTDIR)/usr
-BINDIR ?= $(PREFIX)/bin
+PREFIX ?= /usr
+BINDIR ?= $(DESTDIR)$(PREFIX)/bin
 
 CFLAGS ?= -Wall -Werror
 override CFLAGS += -I../include