tcl: remove redundant file creation

The creation of compat/fixstrtod.c was done back in 2005[1] with no
explanation and has persisted since.  I can't seem to break the build
without this, so it is presumably long obsolete.

[1] https://git.openembedded.org/openembedded/commit/?id=68d6601e8f93243347b58324ce3d4f02eb3a84a9



Signed-off-by: Ross Burton <ross.burton@arm.com>