build.config: Fixing legacy dtc build

When building with legacy build.sh, the host dtc tools are not
generated due to a faulty logic check.

Fix the logic check and make the build environment explicit.

Change-Id: Id4f58fd812f3135379f47a22025f3030ecf68b58
Signed-off-by: John Moon <quic_johmoo@quicinc.com>

build.config.msm.common

@@ -18,11 +18,12 @@ CONFIG_TARGET=msm.${MSM_ARCH}
 ##
 function compile_external_dtc() {
   (
-    OUT_DIR=${COMMON_OUT_DIR}/external/dtc
-    if [ ! -d "$OUT_DIR" ]; then
+    # Bazel builds dtc with its own rule, so skip if building with Bazel
+    if [ -n "$BUILDING_WITH_BAZEL" ]; then
         return
     fi
 
+    OUT_DIR=${COMMON_OUT_DIR}/external/dtc
     [ "${SKIP_MRPROPER}" != "1" ] && rm -rf ${OUT_DIR}
     cd ${ROOT_DIR}/external/dtc
     DTC_MAKE_ARGS=("CC=${HOSTCC}" "AR=${AR}")

msm_kernel.bzl

@@ -39,6 +39,18 @@ def define_build_config(
       variant: variant of kernel to build (e.g. "gki")
     """
 
+    # Top-level variables set in build.config
+    native.genrule(
+        name = "{}_top_level_config".format(target),
+        srcs = [],
+        outs = ["build.config.bazel.top.level.{}".format(target)],
+        cmd_bash = """
+          {
+            echo BUILDING_WITH_BAZEL=true
+          } > "$@"
+        """
+    )
+
     # Remove sourcing lines from build config since we're just concatenating fragments below
     native.genrule(
         name = "{}_build_config_common_without_source".format(target),
@@ -93,6 +105,7 @@ EOF
         name = "{}_build_config".format(target),
         srcs = [
             # do not sort
+            ":{}_top_level_config".format(target),
             "build.config.constants",
             ":{}_build_config_common_without_source".format(target),
             "build.config.aarch64",