proxychains-ng: ensure cross compiler is used

Fixes http://autobuild.buildroot.org/results/e184fcb1c100e9d8aa3d9f18a8caee8c0839e207



Contrary to what the .mk file states, proxychains-ng doesn't use autotools.
Instead it uses a handwritten configure script, so convert it to
generic-package.

This handwritten configure script generates config.mak which is then
included by the Makefile. Unfortunately config.mak does:

CC ?= $(TARGET_CC)

But as make sets CC to 'cc' by default, this never does anything - So
it ends up using the host compiler (and target CFLAGS), breaking the build.

Fix it by passing the correct CC setting at build time as well.

While we're at it, also cleanup the package by using 'make install-config'
to install the configuration file.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>