Inlining problem of core.bitops

[jkrempus at gmail.com]

In LDC, core.bitop.bsf is just an ordinary function compiled in 
libdruntime-ldc.a. Since bitop.d isn't on the command line, LDC uses the 
precompiled code in the library, which can't be inlined. You can get it 
to inline bsf by putting bitop.d on the command line:

ldmd2 -O -release -inline -output-s test.d /opt/ldc/include/d/core/bitop.d

_D4test4foo1FNaNbxkZk:
    .cfi_startproc
    movl	%edi, %eax
    bsfq	%rax, %rax
    ret

It inlines llvm_cttz because that is an llvm intrinsic.