Rewrote configure script from scratch. It now has several useful
features

- Detects LLVM bitcode compiler independent of what was detected
  at LLVM Configure time.

- Detected compiler is tested.

- Supports building native or bitcode library.

- Logging output

- Removed seperate Rules.mak.* files. Now there is just one.

- Changed configuration method to make minimal changes to Rules.mak.
  Instead a file Makefile.klee (created by configure) in included
  by Rules.mak. This is done so that merging with upstream uclibc
  will be easier.
Added --enable-assertions and --enable-debug flags to configure script.
Use debug build by default instead of release.

It seems the release mode build of uclibc breaks some KLEE
tests and I don't feel like debugging those right now.
Remove some stray build files (removed with make clean)
Added make menuconfig build files to gitignore
Remove stray build file.
Moved x86_64 .config file into a directory for pre-made .config
files for klee. i686 support has not been added yet!

The configure script copies the relevant .config to the uclibc
root directory based on the detected architecture.
This behaviour can be disabled using the --disable-prebuilt-config
flag so that the user is free to make their own .config
Added i686 support for pre-made .config file.
Fixed build on i686 on Linux 3.11.6.

This fix corresponds to the fix applied in 2262ed698419f2d3ed7645bd6b679ab92e6892eb
but is for i686 rather than x86_64