Fix regal build after recent clang change. NFC (#21885)

There appears to be a typo in Regal's linear.h:

```
linear.h:585:26: error: no member named 'negate' in 'Vec4<T>'; did you mean 'Negate'?
  585 |       Vec4 rv(*this); rv.negate(); return rv;
      |                          ^~~~~~
      |                          Negate
linear.h:534:11: note: 'Negate' declared here
  534 |     void  Negate() {
```

This was not an issue until llvm/llvm-project#90152
landed.

Adding `-fdelayed-template-parsing` seems to fix the issue.

Author: sbc100

tools/ports/regal.py

@@ -107,7 +107,8 @@ def create(final):
       '-I' + source_path_lookup3,
       '-I' + source_path_boost,
       '-Wno-deprecated-register',
-      '-Wno-unused-parameter'
+      '-Wno-unused-parameter',
+      '-fdelayed-template-parsing',
     ]
     if settings.PTHREADS:
       flags += ['-pthread']