In recent releases both the PBMS and PBXT engines have been using a configuration flag "--with-mysql" to tell the build where to find the MySQL tree. We then looked inside the 'config.status' file generated when MySQL was configured to get the build options, most importantly the compiler options used. We had been doing this using 'grep' and 'sed'. The problem we soon discovered was that the format of the 'config.status' file changes quit frequently with different versions of 'autoconf'.
With the help of the good people on the 'autoconf' forum I discovered that you can ask 'config.status' to give you the value of a single substitution. So to get the value for CFLAGS you enter:
echo '@CFLAGS@' | config.status --file-
and it will print out a line with the CFLAGS.
I understand that this feature which has always existed is now being added to the 'autoconf' documentation.
Using this when configuring your build guarantees that your compiler options match that of MySQL and avoids those nasty bugs where structure alignments do not match because of different compiler settings.
I hope this helps someone out there.