newlib: Remove fcntl() implementation from libc

Allows fcntl() implementation in vfs to be used.

Closes https://github.com/espressif/esp-idf/issues/1070

Note this is different to the other libc file-related syscalls, as there is no
reent structure involved.

components/newlib/libc_discard.list

@@ -77,6 +77,7 @@ lib_a-close.o
 lib_a-creat.o
 lib_a-environ.o
 lib_a-fclose.o
+lib_a-fcntlr.o
 lib_a-isalnum.o
 lib_a-isalpha.o
 lib_a-isascii.o
@@ -131,6 +132,7 @@ lib_a-strupr.o
 lib_a-stdio.o
 lib_a-syssbrk.o
 lib_a-sysclose.o
+lib_a-sysfcntl.o
 lib_a-sysopen.o
 creat.o
 lib_a-sysread.o