[libvirt] wrong warning flags for clang

Appears that configure doesn't properly detect the case when clang is used instead of gcc: CC=clang ./configure runs fine, but produces a long list of warning flags that clang doesn't support: configure: Warning Flags: -W -Waddress -Wall -Warray-bounds -Wattributes -Wbad-function-cast ... trimmed ... At some point, compilation fails: CC libvirt_util_la-viralloc.lo clang: error: unknown warning option '-Wclobbered' [-Werror,-Wunknown-warning-option] clang: error: unknown warning option '-Wcoverage-mismatch'; did you mean '-Wpointer-type-mismatch'? [-Werror,-Wunknown-warning-option] and many other similar errors. Any idea what would be a proper fix for that? Roman Bogorodskiy