Make musl a native libc.

--- substratevm/src/com.oracle.svm.core.posix/src/com/oracle/svm/core/posix/linux/libc/MuslLibC.java.orig
+++ substratevm/src/com.oracle.svm.core.posix/src/com/oracle/svm/core/posix/linux/libc/MuslLibC.java
@@ -43,13 +43,12 @@
 
     @Override
     public List<String> getAdditionalQueryCodeCompilerOptions() {
-        /* Avoid the dependency to muslc for builds cross compiling to muslc. */
-        return Collections.singletonList("--static");
+        return Collections.emptyList();
     }
 
     @Override
     public String getTargetCompiler() {
-        return "musl-gcc";
+        return "gcc";
     }
 
     @Override
@@ -59,14 +58,11 @@
 
     @Override
     public boolean requiresLibCSpecificStaticJDKLibraries() {
-        return true;
+        return false;
     }
 
     @Override
     public void checkIfLibCSupported() {
-        if (!SubstrateOptions.StaticExecutable.getValue()) {
-            throw UserError.abort("Musl can only be used for statically linked executables.");
-        }
         if (JavaVersionUtil.JAVA_SPEC != 11) {
             throw UserError.abort("Musl can only be used with labsjdk 11.");
         }
--- substratevm/src/com.oracle.svm.native.jvm.posix/src/JvmFuncs.c.orig
+++ substratevm/src/com.oracle.svm.native.jvm.posix/src/JvmFuncs.c
@@ -128,7 +128,7 @@
     return listen(fd, count);
 }
 
-JNIEXPORT int JNICALL JVM_Send(int fd, char* buf, size_t nBytes, uint flags) {
+JNIEXPORT int JNICALL JVM_Send(int fd, char* buf, size_t nBytes, unsigned int flags) {
     RESTARTABLE_RETURN_INT(send(fd, buf, nBytes, flags));
 }
 
--- substratevm/src/com.oracle.svm.core.posix/src/com/oracle/svm/core/posix/linux/libc/LibCFeature.java.orig
+++ substratevm/src/com.oracle.svm.core.posix/src/com/oracle/svm/core/posix/linux/libc/LibCFeature.java
@@ -55,7 +55,7 @@
             @Override
             public String getValueOrDefault(UnmodifiableEconomicMap<OptionKey<?>, Object> values) {
                 if (!values.containsKey(this)) {
-                    return Platform.includedIn(Platform.ANDROID.class) ? "bionic" : "glibc";
+                    return Platform.includedIn(Platform.ANDROID.class) ? "bionic" : "musl";
                 }
                 return (String) values.get(this);
             }