Remove unused Makefile.

The usage of lib/kernel/Makefile.host.am has been removed
since dd625107.
Remove trailing whitespace in configure.ac.
Remove trailing whitespace in lib/llvmopencl/Makefile.am
Remove the mixture of space and tab.
Split llvmopencl autoconf files.
Fix the cross compilation.
Move recursive configuration out of makefile.
Remove unnecessary echo.
Cleanup configure.ac.
Be strict on error in script.
Replace LLVM_OPT with OPT and remove LLVM_OPT.
Share the common m4 macro directory.
Cleanup llvmopencl.so configure script.
Allow cross compilation.
Add output filename if it is not specified by the command line options.
Fix the missing @LLVM_LIBS@.

The @LLVM_LIBS@ was added in configure.ac, but was
not copied to lib/llvmopencl/configure.ac.