Do not use getenv() in Tizen GN config (#26411)

Using getenv is discouraged, because it will get the value from the
environment of the build system only on first use. Any environment
changes after that will not be reflected in the build.

build/config/tizen/config.gni

@@ -14,8 +14,8 @@
 
 declare_args() {
   # Location of Tizen SDK
-  tizen_sdk_root = getenv("TIZEN_SDK_ROOT")
+  tizen_sdk_root = ""
 
   # Location of Tizen SDK sysroot
-  tizen_sdk_sysroot = getenv("TIZEN_SDK_SYSROOT")
+  tizen_sdk_sysroot = ""
 }

src/test_driver/tizen/README.md

@@ -47,7 +47,10 @@ argument of the `gn gen` command.
 # Generate test target
 gn gen --check --fail-on-unused-args \
     --root="$PWD/src/test_driver/tizen" \
-    --args="target_os=\"tizen\" target_cpu=\"arm\" chip_config_network_layer_ble=false" \
+    --args="target_os=\"tizen\" target_cpu=\"arm\" \
+        tizen_sdk_root=\"$TIZEN_SDK_ROOT\" \
+        tizen_sdk_sysroot=\"$TIZEN_SDK_SYSROOT\"
+        chip_config_network_layer_ble=false" \
     out/tizen-check
 # Run Tizen QEMU-based tests
 ninja -C out/tizen-check check