[ndk][conf] Fix Canadian build.

1. Add new two new flags: CFLAGS_FOR_BUILD and LDFLAGS_FOR_BUILD
   and use them in $BUILD_CC test.

2. Unset $LDFLAGS in cross-compile-build-tools.

3. $ARCH can be overrided by environment variable.

Cherry-picked from release_33 branch.
Regenerated with ./autoconf/AutoRegen.sh.

Conflicts:
	configure
	projects/sample/configure

Change-Id: I81ad0aa4fc5fa1111c6bd9b56be2c703a51f9fbe