Fix export of xsltExtMarker on Windows
- libxslt/preproc.h:
(xsltExtMarker): Change
externtoXSLTPUBVARso this variable is exported consistently on all platforms. This regressed in commit 44496bf3.
extern to XSLTPUBVAR so this
variable is exported consistently on all platforms. This
regressed in commit 44496bf3.