InnoDB fails to start under TSan on x86-64

A WITH_TSAN=ON build of 11.8.9 on x86_64 Linux fails to start with the default configuration:

[ERROR] InnoDB: Cannot map innodb_buffer_pool_size_max=8388608m

Since the buffer pool rework, innodb_buffer_pool_size_max defaults to size_in_bytes_max_default = 8ULL << 40 (buf0buf.h), and buf_pool_t::create() reserves the whole range up front via my_large_virtual_alloc(). TSan's x86_64 application address-space windows top out around 4 TiB, so the 8 TiB reservation always fails:

• the constrained-environment carve-out in buf0buf.h (#if SIZEOF_SIZE_T < 8 || defined _AIX || defined HAVE_valgrind) zeroes the default for 32-bit/AIX/Valgrind builds, but not for TSan;
• the shrink-and-retry fallback in buf_pool_t::create() (max(1ULL << 37, requested)) is compiled only for aarch64/riscv/mips/loongarch, so x86_64 goes straight to the oom path;
• the RLIMIT_AS/4 clamp in innodb_init_params() does not apply with an unlimited address-space rlimit (the usual CI container state).