llvm/clang: Upgrade to 21.1.5 release

llvm/clang: Upgrade to 21.1.5 release

Brings following bugfixes on top of 21.1.4

8e2cd28cd4ba (HEAD, tag: llvmorg-21.1.5) [OpenMP] Fix preprocessor mismatches between include and usages of hwloc (#158349)
df3145bf4239 [clang-shlib] Fix linking libclang-cpp on Haiku (#156401)
6bb6ffef0a5d [LLD][COFF] Fix manifest UAC trustInfo namespace (#165285)
0921531330ad [llvm-objcopy][COFF] Update .symidx values after stripping (#153322)
c346c16f93d5 [BPF] Do not emit names for PTR, CONST, VOLATILE and RESTRICT BTF types (#163174)
11ef7520536c [BPF] Support for `DW_TAG_variant_part` in BTF generation  (#155783)
495a2ab653ae [Hexagon] Add REQUIRES: asserts to test
a2178ebcb02a [Hexagon] Incorrect MIR after "hexinsert" pass (#164021)
04102d998d0e [AArch64][llvm] Relax mandatory features for Armv9.6-A (#163973)
5c802f9eac66 [Clang] Do not warn on UTF-16 -> UTF-32 conversions. (#163927)
e94561caef48 workflows/release-documentation: Allow secrets pass through from calling workflow (#162765)
1600cf040584 [Github] Only look at previous commit for MacOS Premerge (#164483)
cd7d2db5a50c [lld][test] Fix AArch64 build attribute test cleanup
2cdfa9d9383c [X86] Use pseudo instructions to zero registers in `buildClearRegister` (#163358)
9faef12c7209 [sancov] Fix stack-depth tracking to use debug locations (#162428)
45afac62e373 Bump version to 21.1.5

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>