Revert "make it possible to do 'make -C sw/' even with builddir!=srcdir"

This reverts commit 11e881a6, which assumed that
"all the Makefile's using it are in builddir/<module>/", which is not the case
for the external/ sub-modules.

autogen.sh

@@ -135,13 +135,6 @@ if ($src_path ne $build_path)
 {
     system ("ln -sf $src_path/configure.ac configure.ac");
     system ("ln -sf $src_path/g g");
-    my @modules = <$src_path/*/Makefile>;
-    foreach my $module (@modules)
-    {
-        my $dir = basename (dirname ($module));
-        mkdir ($dir);
-        system ("ln -sf $src_path/$dir/Makefile $dir/Makefile");
-    }
 }
 system ("$aclocal $aclocal_flags") && die "Failed to run aclocal";
 unlink ("configure");

solenv/gbuild/partial_build.mk

@@ -22,7 +22,7 @@ gb_Side:=host
 endif
 
 ifeq (,$(BUILDDIR))
-BUILDDIR := $(dir $(abspath $(firstword $(MAKEFILE_LIST))))..
+BUILDDIR := $(dir $(realpath $(lastword $(MAKEFILE_LIST))))../..
 endif
 
 ifeq ($(BUILD_TYPE),)