add getCompiler and getLinker methods, to abstract from XSD.
add calc_source_md5 as it's more convenient especially for embedded
targets to add -DPLC_MD5="something" option at compile time than
to mess with editing binary.
add some more helper methods

     1

     2

                  <xsd:element name="Linux">

     3

                    <xsd:complexType>

     4

                      %(toolchain_gcc)s

     5

                    </xsd:complexType>

     6

                  </xsd:element>