Build error on Android

I'm getting the error message below using "rake run:android --trace".

Android NDK: 17c (15c NDK works).
Rhodes: Latest in 6-1-Stable branch.

build.yml:

android:
minSDK: 26
targetSDK: 28
android_title: 0
manifest_template: "AndroidManifest.erb"
abis:
- arm
- x86
version: "8.1.0"
emulator: "Nexus_5X_API_27"

rhobuild.yml:

---
env:
paths:
java: "/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/bin"
android: "/Users/username/Library/Android/sdk"
android-ndk: "/Users/username/Library/Android/ndk/r17c"
app: "/Users/username/Documents/MyApps/MyApp"
build:
wmpath: platform/wm
wp8path: platform/wp8
androidpath: platform/android
iphonepath: platform/iphone
android:
excludedirs:
all:
- "**/.*.swo"
- "**/.*.swn"
- "**/.DS_Store"

Error Message:

[DEBUG] config:android:app_config| $app_config['extensions'] : ["coreapi", "decryptstub", "json", "rholang", "audiocapture", "mediacapture", "mediaplayer"]
[DEBUG] config:android:app_config| $app_config['capabilities'] : ["gps", "camera", "network_state", "vibrate", "sdcard", "hardware_acceleration"]
[INFO] config:android:app_config| +++ API LEVEL of /Users/username/Library/Android/sdk/platforms/android-27: 27
[INFO] config:android:app_config| +++ API LEVEL of /Users/username/Library/Android/sdk/platforms/android-28: 28
[INFO] config:android:app_config| Use Google addon API (1): false
[INFO] config:android:app_config| Using Android SDK build-tools: 28.0.3
[DEBUG] config:android:app_config| Parsing version for: sdklib-26.0.0-dev
[DEBUG] config:android:app_config| Parsed version for /Users/username/Library/Android/sdk/tools/lib/sdklib-26.0.0-dev.jar: 26.0.0
[INFO] config:android:app_config| Using SDK library: /Users/username/Library/Android/sdk/tools/lib/sdklib-26.0.0-dev.jar
[INFO] config:android:app_config| Use Google addon API (2): false
[INFO] config:android:app_config| $vendor = coursewalk
[INFO] config:android:app_config| $app_package_name = com.coursewalk.coursewalk
[INFO] config:android:app_config| Adding maven dependency for .rho: com.android.support:support-v4:25.2.0
.....
In file included from /Users/username/GitHub/rhodes/platform/shared/ruby/include/ruby/ruby.h:36:0,
from /Users/username/GitHub/rhodes/platform/shared/ruby/include/ruby.h:33,
from ext/shared/generated/system_ruby_api.c:1:
/Users/username/GitHub/rhodes/platform/shared/ruby/include/ruby/defines.h:26:19: fatal error: stdio.h: No such file or directory
#include <stdio.h>
^
compilation terminated.
rake aborted!
Compilation failed: ext/shared/InitExtension.cpp