Changes

[clangd] Trivial: Documentation fix in ASTSignals.

[gn build] Port 2f395b7092bd

[flang] Fix some module file issues exposed by Whizard

Generic type-bound interfaces for user-defined operators need to be formatted
as "OPERATOR(.op.)", not just ".op."

PRIVATE generics need to be marked as such.

Declaration ordering: when a generic interface shadows a
derived type of the same name, it needs to be emitted to the
module file at the point of definition of the derived type;
otherwise, the derived type's definition may appear after its
first use.

The module symbol for a module read from a module file needs
to be marked as coming from a module file before semantic
processing is performed on the contents of the module so that
any special handling for declarations in module files can be
properly activated.

IMPORT statements were sometimes missing for use-associated
symbols in surrounding scopes; fine-tune NeedImport().

Differential Revision: https://reviews.llvm.org/D94636

[NFC] Disallow unused prefixes under MC/AArch64

Differential Revision: https://reviews.llvm.org/D94616

[NewPM] Fix placement of LoopFlatten

https://reviews.llvm.org/D90402 was inconsistent with where it put
LoopFlatten between the two pass managers. It also missed adding it to
the non-O1 function simplification pipeline.

PR48738

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D94650

[X86][AVX] Adjust unsigned saturation downconvert negative test

D87145 was showing that this test (added in D45315) could always be constant folded (with suitable value tracking).

What we actually needed was smax(smin()) negative test coverage, the invert of negative_test2_smax_usat_trunc_wb_256_mem, so I've tweaked the test to provide that instead.