fix regression introduced by changeset: 1431:28e9d479aa65 [Use '-p' command line option when running matiec (iec2c)]
Variable matiec_flags in c_ext.py and PythonFileCTNMixin.py is not
used for flags for matiec (IEC to C compiler) actually, but it's used
to compile C-code generated for extensions using normal C-compiler,
like gcc.
<xsd:attribute name="Compiler" type="xsd:string" use="optional" default="gcc"/>
<xsd:attribute name="CFLAGS" type="xsd:string" use="optional" default=""/>
<xsd:attribute name="Linker" type="xsd:string" use="optional" default="gcc"/>
<xsd:attribute name="LDFLAGS" type="xsd:string" use="optional" default=""/>