As discussed in the PR
https://github.com/openjdk/jdk/pull/27078#issuecomment-3267427085
"This patch removed the VARHANDLES_GENSRC_DIR variable used by VarHandleGuards generation."

resulting in errors like this

[2025-09-08T17:07:28,796Z] Exception in thread "main" java.nio.file.AccessDeniedException: /VarHandleGuards.java
[2025-09-08T17:07:28,797Z] at java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:90)
[2025-09-08T17:07:28,797Z] at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:106)
[2025-09-08T17:07:28,797Z] at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111)
[2025-09-08T17:07:28,797Z] at java.base/sun.nio.fs.UnixFileSystemProvider.newFileChannel(UnixFileSystemProvider.java:213)
[2025-09-08T17:07:28,797Z] at java.base/sun.nio.fs.UnixFileSystemProvider.newByteChannel(UnixFileSystemProvider.java:244)
[2025-09-08T17:07:28,797Z] at java.base/java.nio.file.spi.FileSystemProvider.newOutputStream(FileSystemProvider.java:426)
[2025-09-08T17:07:28,797Z] at java.base/java.nio.file.Files.newOutputStream(Files.java:215)
[2025-09-08T17:07:28,798Z] at java.base/java.nio.file.Files.newBufferedWriter(Files.java:2722)
[2025-09-08T17:07:28,798Z] at build.tools.methodhandle.VarHandleGuardMethodGenerator.main(VarHandleGuardMethodGenerator.java:173)
[2025-09-08T17:07:28,804Z] make[3]: *** [/VarHandleGuards.java] Error 1
[2025-09-08T17:07:28,804Z] gensrc/GensrcVarHandles.gmk:163: recipe for target '/VarHandleGuards.java' failed
[2025-09-08T17:07:28,806Z] make[2]: *** [java.base-gensrc-src] Error 2