glibc-compat: add static-link mmap shim (32-bit off_t for vendor V2 blobs)

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Summary

Mirror of #2000 but for glibc vendor binaries (V2 SoCs like hi3520dv200).

Vendor glibc binaries from the V2 era (`libmpi.so` etc.) were built without `_FILE_OFFSET_BITS=64` — their `mmap()` import takes a 32-bit `off_t`. musl's `mmap()` exports 64-bit `off_t`. When libmpi dynamic-links against musl, the high 32 bits of the offset come from uninitialised stack; the kernel sees a garbage pgoff and rejects with `EINVAL`.

Symptom on hi3520dv200: every `HI_MPI_VENC_CreateChn` returns `0xa007800c` (`EN_ERR_VENC_NOMEM`) because libmpi can't mmap the model_buf via `/dev/venc`. Confirmed via an `LD_PRELOAD` trace shim that wraps `mmap()`:

```
mmap(fd=28[/dev/venc], off=0x402b65d8, len=229376) = -1 errno=22 EINVAL
mmap err,page addr:-1896943616 u32PagePhy size:114688
VENC: CreateChn(0) 0xa007800c
```

`0x402b65d8` is a userspace VA (lower 12 bits constant `0x5d8`, upper bits vary between runs with ASLR) — pure stack garbage. The vendor's printed "page addr / u32PagePhy size" values are libmpi-internal state, not the real mmap args, so the message is misleading.

Fix

Mirror PR #2000's pattern, scoped to glibc vendor blobs:

• `glibc-compat/src/glibc-compat-static.c`: new file, `mmap()` / `mmap64()` wrappers that take `uint32_t offset` and go straight to `SYS_mmap2` with `offset >> 12` as pgoff, bypassing musl's libc wrapper entirely.
• `glibc-compat/src/Makefile`: build both `libglibc-compat.so` (the existing `__xstat`/`__isoc99_sscanf` shim) and the new `libglibc-compat-static.a`.
• `glibc-compat/glibc-compat.mk`: `GLIBC_COMPAT_INSTALL_STAGING = YES` + `INSTALL_STAGING_CMDS` so dependent packages can link `-lglibc-compat-static`.
• `Makefile` (`BUNDLE_SDK`): produce `libglibc-compat.so` and `libglibc-compat-static.a` in the published toolchain SDK tarball next to the existing uclibc-compat ones.

The wrapper must be statically linked into the consumer executable. Putting it in a shared library would override musl's mmap process-wide and break musl's own internal callers (malloc, dlopen, …) — that's exactly the bug PR #2000 fixed for uclibc-compat.

Why static linking works

The dynamic linker resolves an undefined import like `mmap` from libmpi.so by walking the global symbol scope: the executable first, then `DT_NEEDED` libraries in order. With `-Wl,--export-dynamic-symbol=mmap` on the executable (or just having the symbol from a static lib that gets pulled in via reference), the executable's `mmap` enters its `.dynsym` and libmpi binds against it instead of musl. musl's own internal mmap calls still bind locally because musl uses internal versions / direct syscalls and isn't subject to symbol interposition for its own callers.

Test plan

• `make BOARD=hi3520dv200_lite` builds clean.
• `output-hi3520dv200/per-package/glibc-compat/host//sysroot/usr/lib/libglibc-compat-static.a` exists (staging install works).
• Local test: consumer app (the dvr_home demo at `~/hifb-demo`) with the mmap shim statically linked + `-Wl,--export-dynamic-symbol=mmap` makes `HI_MPI_VENC_CreateChn` succeed on all 4 channels. Trace shim now shows the syscall reaching the kernel with a valid pgoff and returning a valid mapping.
• CI: SDK build matrix for hi3520dv200_lite (will be wired in a follow-up — currently absent because hi3520dv200 had no opensdk wiring until hisilicon-opensdk: wire hi3520dv200 (replace 4 vendor blobs with source-built) #2109).
• Cross-platform regression check: cv100/ev200/cv500 unaffected (BUNDLE_SDK now also writes libglibc-compat.{so,a} but those families don't link against it).

Refs: #1992 (toolchain ABI audit), #1993 (cv100 stat shim), #2000 (cv100 static-link split), #2109 (hi3520dv200 opensdk wiring that built on top of glibc-compat).