Update the OpenCL Hpp header to version 2.0.15

[SteveBronder]

Summary

Updates the OpenCL HPP headers to the latest release provided by https://github.com/KhronosGroup/OpenCL-CLHPP/tags

This fixes a bug where, with GPUs that support OpenCL 3.0, the current headers can throw an error because they did not know that 3.0 was a possible version.

Tests

No new tests

Side Effects

Yes, now instead of using cl2.hpp we use opencl.hpp

Release notes

Update the OpenCL HPP headers

Checklist

• Math issue #(issue number)

• Copyright holder: Steve Bronder

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	3.43	3.46	0.99	-0.82% slower
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.96	-4.32% slower
eight_schools/eight_schools.stan	0.09	0.09	1.0	-0.1% slower
gp_regr/gp_regr.stan	0.14	0.14	1.01	1.43% faster
irt_2pl/irt_2pl.stan	5.04	5.16	0.98	-2.3% slower
performance.compilation	90.93	88.98	1.02	2.13% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	8.13	8.29	0.98	-2.02% slower
pkpd/one_comp_mm_elim_abs.stan	29.46	30.81	0.96	-4.56% slower
sir/sir.stan	119.76	121.18	0.99	-1.18% slower
gp_regr/gen_gp_data.stan	0.03	0.03	0.98	-2.37% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	2.98	3.02	0.99	-1.48% slower
pkpd/sim_one_comp_mm_elim_abs.stan	0.4	0.38	1.04	4.17% faster
arK/arK.stan	2.04	2.03	1.0	0.29% faster
arma/arma.stan	0.25	0.25	1.02	2.26% faster
garch/garch.stan	0.61	0.6	1.02	1.97% faster
Mean result: 0.995997285403

---

Jenkins Console Log
Blue Ocean
Commit hash: 5810ff7

---

Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

[rok-cesnovar]

Thanks Steve!

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	3.4	3.46	0.98	-1.94% slower
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.97	-3.1% slower
eight_schools/eight_schools.stan	0.09	0.09	1.04	4.12% faster
gp_regr/gp_regr.stan	0.14	0.14	1.02	1.89% faster
irt_2pl/irt_2pl.stan	5.09	5.12	0.99	-0.61% slower
performance.compilation	91.64	89.08	1.03	2.78% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	8.19	8.19	1.0	0.02% faster
pkpd/one_comp_mm_elim_abs.stan	30.85	29.52	1.05	4.31% faster
sir/sir.stan	117.14	119.57	0.98	-2.08% slower
gp_regr/gen_gp_data.stan	0.03	0.03	0.98	-1.69% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	2.96	2.95	1.0	0.29% faster
pkpd/sim_one_comp_mm_elim_abs.stan	0.37	0.37	1.0	-0.4% slower
arK/arK.stan	2.03	2.06	0.99	-1.47% slower
arma/arma.stan	0.27	0.27	1.0	0.22% faster
garch/garch.stan	0.65	0.65	1.0	0.34% faster
Mean result: 1.00226263126

---

Jenkins Console Log
Blue Ocean
Commit hash: 5810ff7

---

Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix