xcompiler wrapper: workaround file mode issue

Due to a bug [1] in the maven-dependency-plugin on some platforms
for unknown reasons the wrapper scripts loose their execute flag.
This is resolved using the <fileMode> configuration option of the
maven-dependency-plugin.

[1] http://jira.codehaus.org/browse/MDEP-109
Merge branch 'feature/fix-toolchain-wrapper' into development