qemu-helper-native: Re-write bridge helper as C program

The bridge helper program is invoked directly from QEMU when it needs to
attach to a network bridge. As such, it is subject to the environment of
QEMU itself. Specifically, if bridging is enabled with direct rendering
acceleration, QEMU is run with an LD_PRELOAD that attempts to preload
several uninative libraries; however /bin/sh doesn't use the uninative
loader which means it can fail to start with an error like:

 /bin/sh: symbol lookup error: sysroots-uninative/x86_64-linux/lib/librt.so.1: undefined symbol: __libc_unwind_link_get, version GLIBC_PRIVATE

Converting the helper program to a C program resolves this problem
because it will now use the uninative loader so the preload doesn't
cause errors.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit f698e98f)
Signed-off-by: Steve Sakoman <steve@sakoman.com>