clang: Upgrade to 21.1.2 release

clang: Upgrade to 21.1.2 release

Brings following bugfixes on top of 21.1.1

b708aea0bc71 [SCEV] Don't perform implication checks with many predicates (#158652)
77a3b0eda361 [RISCV] Refactor RVV builtin code generation for reduce compilation time [NFC] (#154906)
f14551dbc4e8 [RISCV] Reduce ManualCodeGen for RVV intrinsics with rounding mode. NFC
dcc2c1c933be [RISCV] Reduce ManualCodeGen for segment load/store intrinsics. NFC
e625a781211e [LLVM] Update CUDA ELF flags for their new ABI (#149534)
3e93017936b5 MC: Better handle backslash-escaped symbols (#158780)
bc5e9a5e2009 [MC] Add parseSymbol() helper (NFC) (#158106)
e2e5eb2f1cd9 [Loads] Check for overflow when adding MaxPtrDiff + Offset.
661c387fc2f1 release/21.x: [VPlan] Don't narrow op multiple times in narrowInterleaveGroups.
f5c1b5206cbe [PowerPC] Avoid working on deleted node in ext bool trunc combine (#160050)
db70369f400e [Clang] Fix an error-recovery crash after d1a80dea (#159976)
9c8736f348e0 [ELF] -r/--emit-relocs: Fix crash when processing .rela.text before .text (#156354)
15a31832eab7 [RISCV] Re-work how VWADD_W_VL and similar _W_VL nodes are handled in combineOp_VLToVWOp_VL. (#159205)
f089fb21fffa [LoongArch] Fix MergeBaseOffset for constant pool index operand (#159336)
9eedaf5b1001 [VectorCombine] Fix scalarizeExtExtract for big-endian (#157962)
5af5cfb60d9e [clang-format] Handle C digit separators (#158418)
0174263ac214 Bump version to 21.1.2
ff039a98523f [RISCV] Support PreserveMost calling convention (#148214)
1a644bc50948 [X86] Fix assertion in AVX512 setcc combine due to invalid APInt mask width (#155775)
2c8cb316b5d2 [lldb][test] Only assert function name is in user-code on Darwin platforms
f5ba88341e7c [lldb][test] TestTsanBasic.py: fix function name assertion
faedeb1a2420 [lldb][Instrumentation] Set selected frame to outside sanitizer libraries (#133079)
54896838ca5e [lldb][Target] Clear selected frame index after a StopInfo::PerformAction (#133078)
f4907049285c [Clang][Cygwin] Use correct mangling rule (#158404)

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>