Add newline at the end of source files

[guillaumealgis]

This silences warnings when the -Wnewline-eof compiler flag is enabled.

GCC_WARN_ABOUT_MISSING_NEWLINE
Warn when a source file does not end with a newline. [GCC_WARN_ABOUT_MISSING_NEWLINE, -Wnewline-eof]

IIRC this flag was introduced to be compatible with poorly designed compilers which would struggle to parse files not ending with a newline.