Unbreak compilation on Darwin

Author: Fabian Groffen <grobian@gentoo.org>

--- gdal-2.0.3.old/GDALmake.opt.in
+++ gdal-2.0.3/GDALmake.opt.in
@@ -104,6 +104,10 @@ GDAL_LIB	= 	$(GDAL_ROOT)/libgdal.a
 GDAL_SLIB	=	$(GDAL_ROOT)/libgdal.$(SO_EXT)
 GDAL_SLIB_LINK	=	-L$(GDAL_ROOT) -lgdal
 
+# for building without libtool
+GDAL_SLIB_SO_VER =	$(GDAL_VERSION_MAJOR).$(LIBGDAL_CURRENT).$(LIBGDAL_REVISION)
+GDAL_SLIB_SONAME =	-install_name $(INST_LIB)/libgdal.$(GDAL_VERSION_MAJOR).$(SO_EXT)
+
 # Mac OS X Framework definition
 MACOSX_FRAMEWORK = @MACOSX_FRAMEWORK@
 
--- gdal-2.0.3.old/GNUmakefile
+++ gdal-2.0.3/GNUmakefile
@@ -208,7 +208,7 @@ else
 
 ifeq ($(HAVE_LD_SHARED),yes)
 
-GDAL_SLIB_B	=	$(notdir $(GDAL_SLIB))
+GDAL_SLIB_B	=	libgdal
 
 install-lib:
 
@@ -216,14 +216,14 @@ install-lib:
 ifeq ($(MACOSX_FRAMEWORK),yes)
 	$(INSTALL_LIB) $(GDAL_SLIB) $(DESTDIR)$(INST_LIB)/GDAL
 else
-	rm -f $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B)
-	rm -f $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B).$(GDAL_VERSION_MAJOR)
-	rm -f $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B).$(GDAL_VER)
-	$(INSTALL_LIB) $(GDAL_SLIB) $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B).$(GDAL_VER)
+	rm -f $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B).dylib
+	rm -f $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B).$(GDAL_VERSION_MAJOR).dylib
+	rm -f $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B).$(GDAL_VER).dylib
+	$(INSTALL_LIB) $(GDAL_SLIB) $(DESTDIR)$(INST_LIB)/$(GDAL_SLIB_B).$(GDAL_VER).dylib
 	(cd $(DESTDIR)$(INST_LIB) ; \
-	 ln -s $(GDAL_SLIB_B).$(GDAL_VER) $(GDAL_SLIB_B).$(GDAL_VERSION_MAJOR))
+	 ln -s $(GDAL_SLIB_B).$(GDAL_VER).dylib $(GDAL_SLIB_B).$(GDAL_VERSION_MAJOR).dylib)
 	(cd $(DESTDIR)$(INST_LIB) ; \
-	 ln -s $(GDAL_SLIB_B).$(GDAL_VERSION_MAJOR) $(GDAL_SLIB_B))
+	 ln -s $(GDAL_SLIB_B).$(GDAL_VERSION_MAJOR).dylib $(GDAL_SLIB_B).dylib)
 	$(INSTALL_DIR) $(DESTDIR)$(INST_LIB)/gdalplugins
 endif