Revert "使用NDK r21"

This reverts commit e11b0b1b.

Classes/openal/android/config.h

@@ -93,7 +93,7 @@
 #define HAVE_MODFF
 
 /* Define if we have the log2f function */
-#define HAVE_LOG2F
+/* #undef HAVE_LOG2F */
 
 /* Define if we have the cbrtf function */
 #define HAVE_CBRTF

README.md

@@ -13,7 +13,9 @@ ndk编译环境(请用迅雷，旋风，或者翻墙vpn下载)
     Windows: https://dl.google.com/android/ndk/android-ndk-r9d-windows-x86_64.zip
     
     目前最新ndk
-	https://developer.android.google.cn/ndk/downloads/
+    https://dl.google.com/android/repository/android-ndk-r15b-windows-x86_64.zip
+    https://dl.google.com/android/repository/android-ndk-r15b-darwin-x86_64.zip
+    https://dl.google.com/android/repository/android-ndk-r15b-linux-x86_64.zip
     
 重要
 ---------------------------------------------

libygo/build.gradle

@@ -27,7 +27,6 @@ android {
             res.srcDirs = ['../libcore/src/main/res']
         }
     }
-    ndkVersion = '21.0.6113669'
 }
 
 dependencies {