These modules provide the same functionality as the modules
dtoastr and ldtoastr except for the formatting taking place in the
C locale.
* MODULES.html.sh: Add c-dtoastr and c-ldtoastr.
* lib/c-dtoastr.c, lib/c-ldtoastr.c: New files.
* lib/ftoastr.c: Prefix exported functions when the macro C_LOCALE is
defined. Use c_snprintf and c_strtod/c_strtold instead of
snprintf and strtod/strtold whhen the macro C_LOCALE is defined.
* lib/ftoastr.h: Add prototypes for c_dtoastr and c_ldtoastr.
* modules/c-dtoastr, modules/c-dtoastr-tests, modules/c-ldtoastr,
modules/c-ldtoastr-tests: New files.
* tests/test-c-dtoastr.c, tests/test-c-dtoastr.sh,
tests-c-ldtoastr.c tests-c-ldtoastr.sh: New files.