Building CPP (JNI) and Java on Raspberry/Raspbian

Hello,
there is a Problem building my project on
Linux raspberrypi 5.4.51-v7+ #1327 SMP Thu Jul 23 10:58:46 BST 2020 armv7l GNU/Linux
It’s a Raspberry Pi OS (32-bit) with Desktop - Hardware is Raspberry Pi 3

My project-structure is:
./src/main/resources
./src/main/java
./ws281x/src/main/public
./ws281x/src/main/headers
./ws281x/src/main/cpp

./ws281x/build.gradle

plugins {
id ‘cpp-library’
}

tasks.withType(CppCompile).configureEach {
compilerArgs.add “-I$System.env.JAVA_HOME” + “include”
compilerArgs.add “-I$System.env.JAVA_HOME” + “include/linux”
compilerArgs.add ‘-fpermissive’
dependsOn clean
dependsOn rootProject.compileJava
}

./build.gradle

plugins {
id ‘java’
id ‘application’
}

compileJava {
options.headerOutputDirectory = file("./ws281x/src/main/public/")
dependsOn clean
}

application {
mainClassName = ‘de.mrss.ws281x.stream.ConsoleDemo’
}

jar {
from("./ws281x/build/lib/main/debug") {
include “*.so”
into “lib”
}
manifest {
attributes (
‘Main-Class’: mainClassName
)
}
dependsOn “:ws281x:assemble”
}

repositories {
mavenCentral()
}

dependencies {
implementation group: ‘javax.xml.bind’, name: ‘jaxb-api’, version: ‘2.3.1’
}

./settings.gradle

include ‘ws281x’

If I run gradle jar on an ubuntu-Desktop
Linux Z390F 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
build will successfully end and generates the files i expect (java-build, cpp-build, jar with java and cpp-content). The generated lib won’t work - but this is expected, too.
But on the target-maschine (Raspi) there will be an error:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':ws281x:compileDebugCpp'.
> No tool chain is available to build C++ for host operating system 'Linux' architecture 'arm-v7':
    - Tool chain 'visualCpp' (Visual Studio):
        - Visual Studio is not available on this operating system.
    - Tool chain 'gcc' (GNU GCC):
        - Don't know how to build for host operating system 'Linux' architecture 'arm-v7'.
    - Tool chain 'clang' (Clang):
        - Don't know how to build for host operating system 'Linux' architecture 'arm-v7'.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 24s

What have I to do to let the build succeed on Raspi?

I’m using gradle 6.5.1 (from gradle.org-Download) on both.

I’ve apt-get install(ed) clang, so gcc und clang are available - this doesn’t solve this problem. I’ve no idea, what gradle’s problem might be. On Raspi build of c/cpp is posssible - but gradle won’t…?! Please help…
I did a Build-Scan … hope, those infos help…