Remove jerry-libc (#2332)

Rationale:
- There is no port under targets/ that would use it. All of them
  turn it off when building.
- That's no surprise, as jerry-libc supports no barebone MCUs but
  posix targets with syscalls only. Actually, that's Linux only,
  because macOS builds have turned off the use of jerry-libc a
  while ago.
- And there is no point in maintaining a highly restricted set of
  libc functions: as soon as someone wants to use JerryScript in a
  scenario that needs more functions than jerry-main, they have to
  choose a different libc (most problably the compiler's default
  one).

I think that we should not keep supporting an otherwise unused
library for the purposes of jerry-main on arm/x86/x64-linux  only.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

tools/build.py

@@ -92,8 +92,6 @@ def get_arguments():
                          help=devhelp('build test version of the jerry command line tool (%(choices)s)'))
     compgrp.add_argument('--jerry-ext', metavar='X', choices=['ON', 'OFF'], type=str.upper,
                          help='build jerry-ext (%(choices)s)')
-    compgrp.add_argument('--jerry-libc', metavar='X', choices=['ON', 'OFF'], type=str.upper,
-                         help='build and use jerry-libc (%(choices)s)')
     compgrp.add_argument('--jerry-libm', metavar='X', choices=['ON', 'OFF'], type=str.upper,
                          help='build and use jerry-libm (%(choices)s)')
     compgrp.add_argument('--jerry-port-default', metavar='X', choices=['ON', 'OFF'], type=str.upper,
@@ -178,7 +176,6 @@ def generate_build_options(arguments):
     build_options_append('JERRY_CMDLINE_SNAPSHOT', arguments.jerry_cmdline_snapshot)
     build_options_append('JERRY_CMDLINE_TEST', arguments.jerry_cmdline_test)
     build_options_append('JERRY_EXT', arguments.jerry_ext)
-    build_options_append('JERRY_LIBC', arguments.jerry_libc)
     build_options_append('JERRY_LIBM', arguments.jerry_libm)
     build_options_append('JERRY_PORT_DEFAULT', arguments.jerry_port_default)
     build_options_append('UNITTESTS', arguments.unittests)