Allow -g and -O2 as the arguments of config/xclang.
Test aligned_alloc or posix_memalign with AC_LINK_IFELSE.

AC_COMPILE_IFELSE() won't work because C89 allows the
implicit declartion of functions.  We should test these
functions by linking the code with libc.
Move the #endif in pocl_utils.c.

It seems that #if on line 191 should only apply to
pocl_aligned_free(), thus we have to move the #endif.
Otherwise, pocl_create_event() and pocl_create_command()
won't be compiled and will result in link error.
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.
Remove unused AC_DEFINEs.
Add output filename if it is not specified by the command line options.