<NME> build.gradle
<BEF> apply plugin: 'com.android.library'

android {

    compileSdkVersion 31

android {
    compileSdkVersion 19
    buildToolsVersion "21.1"

    sourceSets {
        main {
        minSdkVersion 21
        //noinspection OldTargetApi
        targetSdkVersion 31
    }

    sourceSets.main {
        manifest.srcFile 'AndroidManifest.xml'
        java.srcDirs = ['src']
        res.srcDirs = ['res']
    }

    lintOptions {
        // generally we accept lint errors when building
        abortOnError false

        // abort release builds in case of FATAL errors
        checkReleaseBuilds true
    }

    dependencies {
        // Android annotations
        implementation 'androidx.annotation:annotation:1.4.0'
    }
}

<MSG> use current build tools version in gradle builds

<DFF> @@ -6,7 +6,7 @@ dependencies {
 
 android {
     compileSdkVersion 19
-    buildToolsVersion "21.1"
+    buildToolsVersion "21.1.2"
 
     sourceSets {
         main {

use current build tools version in gradle builds