needed for spice/common files used by the client, server & qxl driver.
in windows _inline works for both c/c++, while inline is c++ only.
compiling the client with mixed c/c++ code required this define.
When using config.h, it must be the very first include in all source
files since it contains #define that may change the compilation process
(eg libc structure layout changes when it's used to enable large file
support on 32 bit x86 archs). This commit adds it at the beginning
of all .c and .cpp files
