[P4Testgen] Allow building p4testgen without BMV2 target

[vlstill]

• move the tests that use BMV2 from the global testgen test suite to BMV2 folder so they are only enabled if BVM2 is
• fix a cmake problem where including only targets that did not define include directories prevented configuration

Note that this in order to properly test the core of testgen you still need BMV2 testgen target enabled.

fixes #4107

[vlstill]

These are the remaining testgen tests that run with BMV2 disabled:

[==========] Running 14 tests from 2 test suites.
[----------] Global test environment set-up.
[----------] 4 tests from FormatTest
[ RUN      ] FormatTest.Format01
[       OK ] FormatTest.Format01 (0 ms)
[ RUN      ] FormatTest.Format02
[       OK ] FormatTest.Format02 (0 ms)
[ RUN      ] FormatTest.Format03
[       OK ] FormatTest.Format03 (0 ms)
[ RUN      ] FormatTest.Format04
[       OK ] FormatTest.Format04 (0 ms)
[----------] 4 tests from FormatTest (0 ms total)

[----------] 10 tests from TaintTest
[ RUN      ] TaintTest.Taint01
[       OK ] TaintTest.Taint01 (0 ms)
[ RUN      ] TaintTest.Taint02
[       OK ] TaintTest.Taint02 (0 ms)
[ RUN      ] TaintTest.Taint03
[       OK ] TaintTest.Taint03 (0 ms)
[ RUN      ] TaintTest.Taint04
[       OK ] TaintTest.Taint04 (0 ms)
[ RUN      ] TaintTest.Taint05
[       OK ] TaintTest.Taint05 (0 ms)
[ RUN      ] TaintTest.Taint06
[       OK ] TaintTest.Taint06 (0 ms)
[ RUN      ] TaintTest.Taint07
[       OK ] TaintTest.Taint07 (0 ms)
[ RUN      ] TaintTest.Taint08
[       OK ] TaintTest.Taint08 (0 ms)
[ RUN      ] TaintTest.Taint09
[       OK ] TaintTest.Taint09 (0 ms)
[ RUN      ] TaintTest.Taint10
[       OK ] TaintTest.Taint10 (0 ms)
[----------] 10 tests from TaintTest (0 ms total)

[----------] Global test environment tear-down
[==========] 14 tests from 2 test suites ran. (0 ms total)
[  PASSED  ] 14 tests.

[fruffy]

Do these all assume v1model in some way? Might be a flaw in the test design...

[vlstill]

They all fail with messages like this:

[ RUN      ] SmallStepTest.Unary02
unknown file: Failure
C++ exception with description "In file: /home/xstill/repo/p4c/backends/p4tools/modules/testgen/test/gtest_utils.cpp:21
Compiler Bug: Target bmv2/v1model not supported
" thrown in the test body.

Frankly, I'm not entirely sure what is the relation between BMV2 and v1model here :-).

[fruffy]

Hmmm, maybe we should introduce a p4test like extension that works for any target at some point. Just for debugging.

The v1model1 arch is executed on bmv2. Theoretically it could also be v1model on DPDK or Tofino.

[jafingerhut]

I would replace "theoretically" with "hypothetically", or any other word that means "this seems very unlikely to happen, until and unless some very time-rich and motivated volunteers agree to extend P4-DPDK open source implementation to do this".

It is open source, so of course it can happen. I just don't want anyone reading this to mistake the prerequisites required to make it happen. No one I am aware of is signing up for such a project for P4-DPDK.