many `unrecognized opcode` errors when cross compiling for ppc64le

When cross-compiling for ppc64le from x86_64 Ubuntu I get the following errors.

```
[ 0%] Building CXX object _deps/boost-build/libs/atomic/CMakeFiles/boost_atomic.dir/src/lock_pool.cpp.o
[ 0%] Building CXX object _deps/boost-build/libs/chrono/CMakeFiles/boost_chrono.dir/src/chrono.cpp.o
[ 0%] Building C object _deps/boost-build/libs/container/CMakeFiles/boost_container.dir/src/alloc_lib.c.o
[ 0%] Building ASM object _deps/boost-build/libs/context/CMakeFiles/boost_context.dir/src/asm/make_x86_64_sysv_elf_gas.S.o
make_x86_64_sysv_elf_gas.S: Assembler messages:
make_x86_64_sysv_elf_gas.S:59: Error: unrecognized opcode: `movq'
make_x86_64_sysv_elf_gas.S:62: Error: unrecognized opcode: `andq'
make_x86_64_sysv_elf_gas.S:66: Error: unrecognized opcode: `leaq'
make_x86_64_sysv_elf_gas.S:70: Error: unrecognized opcode: `movq'
make_x86_64_sysv_elf_gas.S:73: Error: unrecognized opcode: `stmxcsr'
make_x86_64_sysv_elf_gas.S:75: Error: unrecognized opcode: `fnstcw'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:84: Error: unrecognized opcode: `leaq'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:87: Error: unrecognized opcode: `movq'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:90: Error: unrecognized opcode: `leaq'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:93: Error: unrecognized opcode: `movq'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:133: Error: unrecognized opcode: `ret'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:146: Error: unrecognized opcode: `push'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:149: Error: unrecognized opcode: `jmp'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:154: Error: unrecognized opcode: `xorq'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:156: Error: unrecognized opcode: `call'
/home/runner/work/build-deps/build-deps/build/_deps/boost-src/libs/context/src/asm/make_x86_64_sysv_elf_gas.S:157: Error: unrecognized opcode: `hlt'
make[2]: *** [_deps/boost-build/libs/context/CMakeFiles/boost_context.dir/build.make:78: _deps/boost-build/libs/context/CMakeFiles/boost_context.dir/src/asm/make_x86_64_sysv_elf_gas.S.o] Error 1
make[2]: Leaving directory '/home/runner/work/build-deps/build-deps/build'
make[1]: *** [CMakeFiles/Makefile2:2041: _deps/boost-build/libs/context/CMakeFiles/boost_context.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
```

https://github.com/LizardByte/build-deps/actions/runs/16693866779/job/47255227124?pr=476#step:15:36

I should add that this is with boost 1.87.0, as we're stuck with this version until the codebase is updated to support code that was removed in 1.88+. If this has already been fixed, I apologize.