documentation/poky-ref-manual: Review edits on B and externalsrc.bbclass

I tried to implement some comments by Richard on the B glossary
entry and the externalsrc.bbclass section.  The comments were a bit
confusing to me but the gist of it was I mis-interpreted Richard's
comments on supporting separate directories for B and S.  I had
indicated that autotools-based recipes did this by default, which
was wrong.  What was confusing to me is where the comments should
be.  I ended up putting them in both areas of the reference manual.

(From yocto-docs rev: a2ddc17bd003b116e593f7df0f59d86cfa0e1cd9)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/documentation/poky-ref-manual/ref-classes.xml b/documentation/poky-ref-manual/ref-classes.xml
index 09b3161fb7..e2bf9fed99 100644
--- a/documentation/poky-ref-manual/ref-classes.xml
+++ b/documentation/poky-ref-manual/ref-classes.xml
@@ -567,6 +567,9 @@
         <link linkend='var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></link> variable. 
         When you do, the <link linkend='var-B'><filename>B</filename></link> variable must support the 
         recipe's ability to build variants in different working directories.
+        Most autotools-based recipes support separating these directories.
+        The Yocto Project defaults to using separate directories for <filename>gcc</filename>
+        and some kernel recipes.
         Alternatively, you can make sure that separate recipes exist that each 
         use the <filename>BBCLASSEXTEND</filename> variable to build each variant.
         The separate recipes can inherit a single target recipe.