Add the architecture-specific pieces needed for the ASan and UBSan
sanitizer runtimes to build and run on hexagon-unknown-linux-musl.
Without this patch, building sanitizer runtimes for Hexagon Linux fails
with:
sanitizer_linux.cpp: error: member access into incomplete type
'struct stat64'
because musl libc does not provide struct stat64. This patch routes
Hexagon through the statx() syscall path (like LoongArch) to avoid the
stat64 dependency entirely.
Changes:
* asan_mapping.h: Add ASAN_SHADOW_OFFSET_CONST (0x20000000) for Hexagon
with shadow layout documentation.
* sanitizer_linux.cpp: Implement internal_clone() for Hexagon using
inline assembly (trap0 syscall, generic clone argument order: flags,
stack, ptid, ctid, tls). Route Hexagon through the statx() path for stat
operations since musl lacks struct stat64.
* sanitizer_linux.h: Add Hexagon to the internal_clone() declaration
guard.
* sanitizer_stoptheworld_linux_libcdep.cpp: Add Hexagon to the
StopTheWorld architecture guard with register definitions.
* sanitizer_asm.h: Define ASM_TAIL_CALL as 'jump' for Hexagon.
* CMakeLists.txt: Add -fno-emulated-tls for Hexagon targets. Hexagon
Linux uses native TLS via the UGP register; emulated TLS produces broken
sanitizer runtimes with unresolvable __emutls references.
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