Bazel can't cross-compile the XNNPACK tests

Using Bazel 8.1.1 (also broken under Bazel 7.6.1)

Build command is:
```
bazel build -c opt --config=android_arm64 test:all
```

Example output is:
```
Compiling kai/ukernels/matmul/matmul_clamp_f32_qai8dxp_qsi4c32p/kai_matmul_clamp_f32_qai8dxp4x8_qsi4c32p4x8_8x4x32_neon_i8mm.c failed: (Exit 1): gcc failed: error executing CppCompile command (from target @@+_repo_rules+KleidiAI//kai/ukernels/matmul:i8mm_impl_asm) /usr/bin/gcc -U_FORTIFY_SOURCE -fstack-protector -Wall -Wunused-but-set-parameter -Wno-free-nonheap-object -fno-omit-frame-pointer -g0 -O2 '-D_FORTIFY_SOURCE=1' -DNDEBUG -ffunction-sections ... (remaining 34 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
cc1: error: bad value 'armv8.2-a+i8mm' for '-march=' switch
cc1: note: valid arguments to '-march=' switch are: nocona core2 nehalem corei7 westmere sandybridge corei7-avx ivybridge core-avx-i haswell core-avx2 broadwell skylake skylake-avx512 cannonlake icelake-client rocketlake icelake-server cascadelake tigerlake cooperlake sapphirerapids emeraldrapids alderlake raptorlake meteorlake graniterapids graniterapids-d arrowlake arrowlake-s lunarlake pantherlake bonnell atom silvermont slm goldmont goldmont-plus tremont gracemont sierraforest grandridge clearwaterforest knl knm x86-64 x86-64-v2 x86-64-v3 x86-64-v4 eden-x2 nano nano-1000 nano-2000 nano-3000 nano-x2 eden-x4 nano-x4 lujiazui yongfeng k8 k8-sse3 opteron opteron-sse3 athlon64 athlon64-sse3 athlon-fx amdfam10 barcelona bdver1 bdver2 bdver3 bdver4 znver1 znver2 znver3 znver4 znver5 btver1 btver2 native
Use --verbose_failures to see the command lines of failed build steps.
```

Host is Linux x64. Shouldn't be using GCC - should be using the Android NDK for this. Does anybody use this flow regularly?

`bazel build -c opt --config=android_arm64 //...` and `bazel build -c opt --config=android_arm64 :all` don't work either.