While building x86 with GCC 10.3 works, we get some compilation errors with GCC 11 (tested with GCC 11.2.0):

/home/test/shipilev-jdk/src/java.base/share/native/libjava/jni_util.c: In function 'newString646_US':
/home/test/shipilev-jdk/src/java.base/share/native/libjava/jni_util.c:487:15: error: 'str1' may be used uninitialized [-Werror=maybe-uninitialized]
  487 | result = (*env)->NewString(env, str1, len);
      | ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/test/shipilev-jdk/src/java.base/share/native/libjava/jni_util.c:487:15: note: by argument 2 of type 'const jchar *' {aka 'const short unsigned int *'} to 'struct _jobject *(const struct JNINativeInterface_ **, const jchar *, jsize)' {aka 'struct _jobject *(const struct JNINativeInterface_ **, const short unsigned int *, int)'}

Some of the build failures seem to be related to JDK-8289046 ('this' pointer is null). Fixing JDK-8289046 should also fix these specific failures.