extra/Configs/Config.in: add syncfs() to Linux-specific functions

syncfs() was recently added (commit dfa593d4d).  But man sync(2) specifies
that syncfs() is Linux-specific.  This was overlooked in the original
commit so we add it to the set of Linux-specific functions supported by
uClibc.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>

extra/Configs/Config.in

@@ -1042,8 +1042,9 @@ config UCLIBC_LINUX_SPECIFIC
 	  sched_getaffinity(), sched_setaffinity(), sendfile(),
 	  setfsgid(), setfsuid(), setresgid(), setresuid(),
 	  splice(), vmsplice(), tee(), signalfd(), statfs(),
-	  swapoff(), swapon(), sync_file_range(), _sysctl(),
-	  sysinfo(), timerfd_*(), vhangup(), umount(), umount2()
+	  swapoff(), swapon(), sync_file_range(), syncfs(),
+	  _sysctl(), sysinfo(), timerfd_*(), vhangup(), umount(),
+	  umount2()
 
 config UCLIBC_HAS_GNU_ERROR
 	bool "Support GNU extensions for error-reporting"

libc/sysdeps/linux/common/Makefile.in

@@ -56,6 +56,7 @@ CSRC-$(UCLIBC_LINUX_SPECIFIC) += \
 	swapoff.c \
 	swapon.c \
 	sync_file_range.c \
+	syncfs.c \
 	sysctl.c \
 	sysinfo.c \
 	tee.c \