package/pkg-waf: add support for <pkg>_SUBDIR

In the Buildroot manual, it is specified that the Waf-based
infrastructure supports the <pkg>_SUBDIR variable, which was not true.

This patch:
* makes use of this variable by changing to the given sub-directory
  before executing waf commands,
* documents the usage of <pkg>_SUBDIR in the waf-specific section of
  the manual.

Signed-off-by: Lionel Orry <lionel.orry@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/docs/manual/adding-packages-waf.txt b/docs/manual/adding-packages-waf.txt
index 12e122fb87..ffc004c290 100644
--- a/docs/manual/adding-packages-waf.txt
+++ b/docs/manual/adding-packages-waf.txt
@@ -60,6 +60,12 @@ the generic infrastructure also exist in the Waf infrastructure:
 An additional variable, specific to the Waf infrastructure, can
 also be defined.
 
+* +LIBFOO_SUBDIR+ may contain the name of a subdirectory inside the
+  package that contains the main wscript file. This is useful,
+  if for example, the main wscript file is not at the root of
+  the tree extracted by the tarball. If +HOST_LIBFOO_SUBDIR+ is not
+  specified, it defaults to +LIBFOO_SUBDIR+.
+
 * +LIBFOO_NEEDS_EXTERNAL_WAF+ can be set to +YES+ or +NO+ to tell
   Buildroot to use the bundled +waf+ executable. If set to +NO+, the
   default, then Buildroot will use the waf executable provided in the