Support Bazel 9

Bazel 9 is now released. The only blocker is that BCR `p4runtime 1.5.0`
declares `bazel_compatibility < 9.0.0`. Suppress the check via
`--check_bazel_compatibility=off` until a new p4runtime BCR release is
cut (tracked in p4lang/p4runtime#597). Unlike `git_override`, this flag
works for modules published to the BCR.

Also add a Bazel version matrix to CI (7.x and 9.x), and fix macOS
builds: use Command Line Tools clang to avoid requiring a full Xcode
install, and set `macos_minimum_os=10.15` which is the minimum for
`std::filesystem` support in libc++.

Signed-off-by: Steffen Smolka <steffen.smolka@gmail.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: smolkaj

.bazelrc

@@ -9,3 +9,9 @@ build --host_cxxopt=-std=c++20
 # Force the use of Clang for all builds.
 build --action_env=CC=clang
 build --action_env=CXX=clang++
+
+# macOS: use Command Line Tools clang (avoids requiring a full Xcode install)
+# and raise the deployment target to 10.15, which is the minimum for
+# std::filesystem support in libc++.
+build --repo_env=CC=/usr/bin/clang
+build --macos_minimum_os=10.15

.bazelversion

@@ -1 +1 @@
-8.5.0
+9.0.0

MODULE.bazel

@@ -26,7 +26,7 @@ bazel_dep(name = "rules_license", version = "1.0.0")
 bazel_dep(name = "rules_m4", version = "0.3")
 bazel_dep(name = "rules_proto", version = "7.1.0")
 bazel_dep(name = "z3", version = "4.15.2")
-bazel_dep(name = "p4runtime", version = "1.5.0")
+bazel_dep(name = "p4runtime", version = "1.5.0.bcr.1")
 
 p4c_repositories = use_extension("//bazel:repositories.bzl", "p4c_repositories")
 use_repo(