docs: BSD and Solaris make trailing space macro issue.

[Ralf Wildenhues]

OK to push?

This prepares the next couple of patches.  Yes, it adds a trailing space
in the manual source.  I'm not sure how useful that is, given that it
doesn't survive in the .info output.  Suggestions welcome.

Thanks,
Ralf

    docs: BSD and Solaris make trailing space macro issue.
    
    * doc/autoconf.texi (Trailing whitespace in Make Macros):
    Document issue with trailing whitespace in macro settings.

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index b552883..c537335 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -19853,6 +19853,20 @@ Trailing whitespace in Make Macros
 @noindent
 prints @samp{bar.test .test}.
 
+BSD and Solaris @command{make} implementations do not honor trailing
+whitespace in macro definitions as Posix requires:
+
address@hidden
+# The following line contains a trailing space.
+foo = bar 
+print: ; @@echo $(foo)t
address@hidden example
+
address@hidden
+prints @samp{bart} instead of @samp{bar t}.  To work around this, you
+can use a helper macro as in the previous example.
+
+
 @node Command-line Macros and whitespace
 @section Command-line Macros and whitespace
 @cindex whitespace in command-line macros