Allow setting C++ standard with standard in swift test targets

[peddie]

This is already supported in swift_cc_library and swift_cc_tool.

[peddie]

Hm, I get a bunch of:

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: invalid argument '-std=c++14' not allowed with 'C'
ERROR: /home/peddie/.cache/bazel/_bazel_peddie/d44546e2b755e65528d263d98d986bf0/external/starling/rtklib_rtcm/BUILD.bazel:3:22: Compiling rtklib_rtcm/src/rtcm3e.c failed: (Exit 1): clang failed: error executing command (from target @starling//rtklib_rtcm:rtklib_rtcm) external/rules_swiftnav/cc/toolchains/llvm/x86_64-linux/wrappers/clang -U_FORTIFY_SOURCE '--target=x86_64-unknown-linux-gnu' -U_FORTIFY_SOURCE -fstack-protector -fno-omit-frame-pointer ... (remaining 159 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: invalid argument '-std=c++14' not allowed with 'C'
ERROR: /home/peddie/.cache/bazel/_bazel_peddie/d44546e2b755e65528d263d98d986bf0/external/starling/rtklib_rtcm/BUILD.bazel:3:22: Compiling rtklib_rtcm/src/rtklib_igs/rtklib_preceph.c failed: (Exit 1): clang failed: error executing command (from target @starling//rtklib_rtcm:rtklib_rtcm) external/rules_swiftnav/cc/toolchains/llvm/x86_64-linux/wrappers/clang -U_FORTIFY_SOURCE '--target=x86_64-unknown-linux-gnu' -U_FORTIFY_SOURCE -fstack-protector -fno-omit-frame-pointer ... (remaining 159 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: invalid argument '-std=c++14' not allowed with 'C'
ERROR: /home/peddie/.cache/bazel/_bazel_peddie/d44546e2b755e65528d263d98d986bf0/external/starling/rtklib_rtcm/BUILD.bazel:3:22: Compiling rtklib_rtcm/src/rtcm.c failed: (Exit 1): clang failed: error executing command (from target @starling//rtklib_rtcm:rtklib_rtcm) external/rules_swiftnav/cc/toolchains/llvm/x86_64-linux/wrappers/clang -U_FORTIFY_SOURCE '--target=x86_64-unknown-linux-gnu' -U_FORTIFY_SOURCE -fstack-protector -fno-omit-frame-pointer ... (remaining 159 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: invalid argument '-std=c++14' not allowed with 'C'
ERROR: /home/peddie/.cache/bazel/_bazel_peddie/d44546e2b755e65528d263d98d986bf0/external/starling/rtklib_rtcm/BUILD.bazel:3:22: Compiling rtklib_rtcm/src/rtcm3.c failed: (Exit 1): clang failed: error executing command (from target @starling//rtklib_rtcm:rtklib_rtcm) external/rules_swiftnav/cc/toolchains/llvm/x86_64-linux/wrappers/clang -U_FORTIFY_SOURCE '--target=x86_64-unknown-linux-gnu' -U_FORTIFY_SOURCE -fstack-protector -fno-omit-frame-pointer ... (remaining 159 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: invalid argument '-std=c++14' not allowed with 'C'
ERROR: /home/peddie/.cache/bazel/_bazel_peddie/d44546e2b755e65528d263d98d986bf0/external/starling/rtklib_rtcm/BUILD.bazel:3:22: Compiling rtklib_rtcm/src/rtkcmn.c failed: (Exit 1): clang failed: error executing command (from target @starling//rtklib_rtcm:rtklib_rtcm) external/rules_swiftnav/cc/toolchains/llvm/x86_64-linux/wrappers/clang -U_FORTIFY_SOURCE '--target=x86_64-unknown-linux-gnu' -U_FORTIFY_SOURCE -fstack-protector -fno-omit-frame-pointer ... (remaining 159 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: invalid argument '-std=c++14' not allowed with 'C'
ERROR: /home/peddie/.cache/bazel/_bazel_peddie/d44546e2b755e65528d263d98d986bf0/external/starling/rtklib_rtcm/BUILD.bazel:3:22: Compiling rtklib_rtcm/src/rtklib_igs/rtklib_rinex.c failed: (Exit 1): clang failed: error executing command (from target @starling//rtklib_rtcm:rtklib_rtcm) external/rules_swiftnav/cc/toolchains/llvm/x86_64-linux/wrappers/clang -U_FORTIFY_SOURCE '--target=x86_64-unknown-linux-gnu' -U_FORTIFY_SOURCE -fstack-protector -fno-omit-frame-pointer ... (remaining 159 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: invalid argument '-std=c++14' not allowed with 'C'

[peddie]

Worked around the above errors by only passing this for swift_cc_test but not for the swift_cc_test_library rule for now.