[gn] fix OpenThread build with -Wundef (#5436)

Always define all of OPENTHREAD_{FTD,MTD,RADIO} and add a define for
OPENTHREAD_POSIX.

BUILD.gn

@@ -28,6 +28,7 @@
 import("etc/gn/openthread.gni")
 
 config("openthread_config") {
+  defines = []
   if (openthread_config_file != "") {
     defines += [ "OPENTHREAD_CONFIG_FILE=${openthread_config_file}" ]
   }
@@ -41,15 +42,27 @@ config("openthread_config") {
 }
 
 config("openthread_ftd_config") {
-  defines = [ "OPENTHREAD_FTD=1" ]
+  defines = [
+    "OPENTHREAD_FTD=1",
+    "OPENTHREAD_MTD=0",
+    "OPENTHREAD_RADIO=0",
+  ]
 }
 
 config("openthread_mtd_config") {
-  defines = [ "OPENTHREAD_MTD=1" ]
+  defines = [
+    "OPENTHREAD_MTD=1",
+    "OPENTHREAD_FTD=0",
+    "OPENTHREAD_RADIO=0",
+  ]
 }
 
 config("openthread_radio_config") {
-  defines = [ "OPENTHREAD_RADIO=1" ]
+  defines = [
+    "OPENTHREAD_RADIO=1",
+    "OPENTHREAD_FTD=0",
+    "OPENTHREAD_MTD=0",
+  ]
 }
 
 group("libopenthread-ftd") {

etc/gn/openthread.gni

@@ -55,6 +55,9 @@ declare_args() {
   # Use external mbedtls. If blank, internal mbedtls will be used.
   openthread_external_mbedtls = ""
 
+  # Enable building for POSIX platforms.
+  openthread_posix = current_os == "linux"
+
   # Package name for OpenThread.
   openthread_package_name = "OPENTHREAD"
 

src/cli/BUILD.gn

@@ -25,6 +25,8 @@
 #  POSSIBILITY OF SUCH DAMAGE.
 #
 
+import("../../etc/gn/openthread.gni")
+
 openthread_cli_sources = [
   "cli.cpp",
   "cli.hpp",
@@ -48,14 +50,25 @@ openthread_cli_sources = [
   "x509_cert_key.hpp",
 ]
 
+config("cli_config") {
+  defines = []
+  if (openthread_posix) {
+    defines += ["OPENTHREAD_POSIX=1"]
+  } else {
+    defines += ["OPENTHREAD_POSIX=0"]
+  }
+}
+
 static_library("libopenthread-cli-ftd") {
   sources = openthread_cli_sources
   public_deps = [ "../core:libopenthread-ftd" ]
+  public_configs = [":cli_config"]
   visibility = [ "../../*" ]
 }
 
 static_library("libopenthread-cli-mtd") {
   sources = openthread_cli_sources
   public_deps = [ "../core:libopenthread-mtd" ]
+  public_configs = [":cli_config"]
   visibility = [ "../../*" ]
 }