[pcre-dev] HAVE_CONFIG_H

I agree with Daniel regarding HAVE_CONFIG_H. It should be placed at the
beginning of every file.

In my opinion, ALL Windows operating system specific defines, macros etc
should be moved to the config.h.generic file.

Although the current Windows declspec defines do work, they can be
simplified and located in one place. This will eliminate the need to have to
figure out the order of placement of header files as in, for example, the
ordering of pcre.h and pcre_internal.h. in pcretest.c.

Robert Wishlaw