test: Add check-c run to bazel build.

Makes iterating on both check-c and the toxcore code easier.

testing/BUILD.bazel

@@ -22,6 +22,28 @@ sh_test(
     tags = ["haskell"],
 )
 
+sh_test(
+    name = "c_test",
+    size = "small",
+    srcs = ["//hs-tokstyle/tools:check-c"],
+    args = [
+        "--cc=$(CC)",
+        "-Iexternal/libsodium/include",
+        "-Iexternal/libvpx",
+        "-Iexternal/opus/include",
+        "-Ihs-tokstyle/include",
+    ] + ["$(locations %s)" % f for f in CIMPLE_FILES],
+    data = CIMPLE_FILES + [
+        "//c-toxcore/third_party:headers",
+        "//hs-tokstyle:headers",
+        "@libsodium//:headers",
+        "@libvpx//:headers",
+        "@opus//:headers",
+    ],
+    tags = ["haskell"],
+    toolchains = ["@rules_cc//cc:current_cc_toolchain"],
+)
+
 sh_test(
     name = "cimplefmt_test",
     size = "small",

third_party/BUILD.bazel

@@ -7,3 +7,9 @@ cc_library(
     copts = ["-DCMP_NO_FLOAT"],
     visibility = ["//c-toxcore:__subpackages__"],
 )
+
+filegroup(
+    name = "headers",
+    srcs = ["cmp/cmp.h"],
+    visibility = ["//c-toxcore:__subpackages__"],
+)