Compiling on AIX with xlc17 which contains the new clang 15 frontend
shows the following warnings.

built by make/modules/java.base/Lib.gmk

src/java.base/unix/native/libnet/DefaultProxySelector.c:378:41:22: error: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Werror,-Wdeprecated-non-prototype]
proxies = (*g_proxy_resolver_lookup)(resolver, uri, NULL, &error);
^

src/java.base/unix/native/libnet/NetworkInterface.c:1612:24: error: arithmetic on a pointer to void is a GNU extension [-Werror,-Wgnu-pointer-arith]
end = (void *)nddp + size;
~~~~~~~~~~~~ ^

src/java.base/unix/native/libnio/fs/UnixNativeDispatcher.c:1251:7: error: '_ALLBSD_SOURCE' is not defined, evaluates to 0 [-Werror,-Wundef]
#elif _ALLBSD_SOURCE


built by make/modules/java.base/lib/CoreLibraries.gmk

src/java.base/unix/native/libjava/ProcessHandleImpl_unix.c:638 comparison of integers of different signs: 'int' and 'unsigned long'
if (ret < sizeof(psinfo_t)) {
^

src/java.base/aix/native/libjli/java_md_aix.c:42:38: error: arithmetic on a pointer to void is a GNU extension [-Werror,-Wgnu-pointer-arith]
addr < p->ldinfo_textorg + p->ldinfo_textsize) {
~~~~~~~~~~~~~~~~~ ^

src/java.base/share/native/libzip/zlib/inffast.c:74:20: error: a function definition without a prototype is deprecated in all versions of C and is not supported in C2x [-Werror,-Wdeprecated-non-prototype]
void ZLIB_INTERNAL inflate_fast(strm, start)
^
src/java.base/share/native/libjli/java.c:2311:22: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
vfprintf(stderr, fmt, vl);
^~~

The test library libGetXSpace.c also shows a warning.
In addition, the cast in that lib is wrong, we opened "JDK-8309216 cast from jchar* to char* in test GetXSpace.java" for that.