Fix Makefile to create include directory on install

Also move `Makefile.am` in src to `GNUmakefile.am`

Author: mgreter

Makefile

@@ -244,7 +244,8 @@ $(DESTDIR)$(PREFIX)/lib: $(DESTDIR)$(PREFIX)
 $(DESTDIR)$(PREFIX)/include: $(DESTDIR)$(PREFIX)
 	$(MKDIR) $(DESTDIR)$(PREFIX)/include
 
-$(DESTDIR)$(PREFIX)/include/%.h: include/%.h
+$(DESTDIR)$(PREFIX)/include/%.h: include/%.h \
+                                 $(DESTDIR)$(PREFIX)/include
 	$(INSTALL) -v -m0644 "$<" "$@"
 
 install-headers: $(DESTDIR)$(PREFIX)/include/sass.h \

configure.ac

@@ -137,5 +137,5 @@ AC_SUBST(PACKAGE_VERSION)
 
 AC_MSG_NOTICE([Building libsass ($VERSION)])
 
-AC_CONFIG_FILES([GNUmakefile src/Makefile src/support/libsass.pc])
+AC_CONFIG_FILES([GNUmakefile src/GNUmakefile src/support/libsass.pc])
 AC_OUTPUT

src/Makefile.am renamed to src/GNUmakefile.am

@@ -43,8 +43,8 @@ namespace Sass {
     }
     json_append_member(json_srcmap, "sources", json_includes);
 
-    JsonNode *json_contents = json_mkarray();
     if (include_sources) {
+      JsonNode *json_contents = json_mkarray();
       for (size_t i = 0; i < source_index.size(); ++i) {
         const char *content = sources[source_index[i]];
         JsonNode *json_content = json_mkstring(content);