Allow OCI8 to be DTrace-enabled independently of core PHP's DTrace
status.  The proviso is OCI8 must be built "shared" when DTrace is
enabled.  This implementation (i) works around an incomplete core PHP
solution for extension tracing (ii) avoid any issues with DOF section
location and the complexities of needing to merge all provider .d
files for static builds (iii) allows OCI8 to be DTrace-enabled when
doing PECL installs of OCI8 on PHP versions without core PHP DTrace
support.

This is an initial patch i.e. it will undergo further testing.