On Solaris with version 3.4.6, the ha_example.so shared library is built
with DTrace and the server is built without DTrace support. This occurs
because dtrace.cmake disables DTrace support for 3.4.6, but still set
HAVE_DTRACE, which causes probes_mysql.h to include probes_mysql_dtrace.h
instead of probes_mysql_nodtrace.h.

This patch fixes this by not setting HAVE_DTRACE on Solaris for GCC 3.4.6.