beremiz

file isExecutable
add $(Beremiz installation)/mingw/bin in PATH on Windows platform

This fixes issue if multiple gcc installation are found in user's
PATH. Now gcc from Beremiz is used by default.
<xsd:element name="Xenomai">
<xsd:complexType>
%(toolchain_gcc)s
<xsd:attribute name="XenoConfig" type="xsd:string" use="optional" default="xeno-config"/>
</xsd:complexType>
</xsd:element>