Add support for static-only build

Instead of unconditionally building shared libraries, this patch
improves the libsepol build system with a "STATIC" variable, which
when defined to some non-empty value, will disable the build of shared
libraries. It allows to support cases where the target architecture
does not have support for shared libraries.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/src/Makefile
===================================================================
--- a/src/Makefile
+++ b/src/Makefile
@@ -17,7 +17,12 @@
 CFLAGS ?= -Werror -Wall -W -Wundef -Wshadow -Wmissing-noreturn -Wmissing-format-attribute
 override CFLAGS += -I. -I../include -D_GNU_SOURCE
 
-all: $(LIBA) $(LIBSO) $(LIBPC)
+ALL_TARGETS = $(LIBA) $(LIBPC)
+ifeq ($(STATIC),)
+ALL_TARGETS += $(LIBSO)
+endif
+
+all: $(ALL_TARGETS)
 
 $(LIBA):  $(OBJS)
 	$(AR) rcs $@ $^
@@ -39,11 +44,13 @@
 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) $(LIBDIR)/pkgconfig
+ifeq ($(STATIC),)
+	test -d $(SHLIBDIR) || install -m 755 -d $(SHLIBDIR)
+	install -m 755 $(LIBSO) $(SHLIBDIR)
 	cd $(LIBDIR) && ln -sf ../../`basename $(SHLIBDIR)`/$(LIBSO) $(TARGET)
+endif
 
 relabel:
 	/sbin/restorecon $(SHLIBDIR)/$(LIBSO)