clang: inline asm compatibility with gcc

Hi,

for the Linux kernel development we currently have a discussion about a
memset(0) helper function that in all cirumstances implement memset(0). See
[1].

We identified the following differences between gcc and clang. According to
the clang documentation, clang wants to be highly compatible to gcc.
Therefore, this issue may be of interest.

/*
* Tested following code: