Explanations:
OnlyOffice depends on v8 which needs specific compilation tools under
FreeBSD (native v8 compilation tools are not written for FreeBSD. Thus
under FreeBSD we use node10 available in the FreeBSD port compiled with
the "shared" option.  In that way libnode.so is used in order to get the
v8 code).
Since v8 library is got from FreeBSD ports, we also want to
use the native ICU library, boost library, openssl library etc.
Moreover it lets the sysadmin getting the latest security patches for
these libraries and avoid security holes (without recompiling
onlyoffice).

Correct an error in the code which leads to an error during compilation
with clang.

Correct a syntax error in the code which leads to an error during compilation with clang.
Add _gcvt function which does not exists under FreeBSD.

- Correct syntax error in the code which leads to error when compiling
  with clang (not casting signed 8-bits values greater than 0x80).
- Add a specific code which finds the common working directory (using
  /proc for that purpose under FreeBSD is not possible)

Correct syntax error in the code which leads to an error with clang
compiler: returning NULL (void*) to a variable which is unsigned int