[PATCH v2 1/2] ci: also define CXX environment variable

[Josh Steadmon <steadmon@google.com>]

In a future commit, we will build the fuzzer executables as part of the
default 'make all' target, which requires a C++ compiler. If we do not
explicitly set CXX, it defaults to g++ on GitHub CI. However, this can
lead to incorrect feature detection when CC=clang, since the
'detect-compiler' script only looks at CC. Fix the issue by always
setting CXX to match CC in our CI config.

We only plan on building fuzzers on Linux with the next patch, so for
now, only adjust configuration for the Linux CI jobs.

Signed-off-by: Josh Steadmon <steadmon@google.com>
---
 .github/workflows/main.yml | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 3428773b09..d9986256e6 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -265,42 +265,54 @@ jobs:
         vector:
           - jobname: linux-sha256
             cc: clang
+            cxx: clang++
             pool: ubuntu-latest
           - jobname: linux-reftable
             cc: clang
+            cxx: clang++
             pool: ubuntu-latest
           - jobname: linux-gcc
             cc: gcc
+            cxx: g++
             cc_package: gcc-8
             pool: ubuntu-20.04
           - jobname: linux-TEST-vars
             cc: gcc
+            cxx: g++
             cc_package: gcc-8
             pool: ubuntu-20.04
           - jobname: osx-clang
             cc: clang
+            cxx: clang++
             pool: macos-13
           - jobname: osx-reftable
             cc: clang
+            cxx: clang++
             pool: macos-13
           - jobname: osx-gcc
             cc: gcc
+            cxx: g++
             cc_package: gcc-13
             pool: macos-13
           - jobname: linux-gcc-default
             cc: gcc
+            cxx: g++
             pool: ubuntu-latest
           - jobname: linux-leaks
             cc: gcc
+            cxx: g++
             pool: ubuntu-latest
           - jobname: linux-reftable-leaks
             cc: gcc
+            cxx: g++
             pool: ubuntu-latest
           - jobname: linux-asan-ubsan
             cc: clang
+            cxx: clang++
             pool: ubuntu-latest
     env:
       CC: ${{matrix.vector.cc}}
+      CXX: ${{matrix.vector.cxx}}
       CC_PACKAGE: ${{matrix.vector.cc_package}}
       jobname: ${{matrix.vector.jobname}}
       runs_on_pool: ${{matrix.vector.pool}}
-- 
2.44.0.683.g7961c838ac-goog