arch: loongarch64_nosimd: Pass -mattr=-lsx to the linker plugin for Rust

The "Rust + linker-plugin = LSX in main" issue may haunt all Rust
binaries, even a "hello world" program is proven to be affected.  So
aosc-os-abbs/.../oma is just not the correct location to work it around.
And disabling LTO is overly aggressive, we just need to pass an option
to the linker plugin to disable LSX.

FWIW I'm unsure if we should report this as a Rustc issue.

Signed-off-by: Xi Ruoyao <[email protected]>

Author: xry111

arch/loongarch64_nosimd.sh

@@ -24,3 +24,10 @@ fi
 #   - https://github.com/rust-lang/rust/blob/a932eb36f8adf6c8cdfc450f063943da3112d621/compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_gnu.rs#L18
 #   - https://github.com/llvm/llvm-project/blob/98b895da30c03b7061b8740d91c0e7998e69d091/clang/lib/Driver/ToolChains/Arch/LoongArch.cpp#L133
 RUSTFLAGS_COMMON_ARCH=('-Ctarget-cpu=generic-la64' '-Ctarget-feature=-lsx,+d' '-Clink-arg=-mabi=lp64d')
+
+# Rustc does not apply -Ctarget-feature as an attribute to the main function
+# (the function that __libc_start_call_main calls, not crate::main).  So
+# during LTO, the linker plugin may inline some code into main and vectorize
+# them.  Tell lld to disable LSX unless it's explicitly enabled in the
+# function attribute, so main won't be vectorized.
+RUSTFLAGS_COMMON_ARCH_LTO=('-Clink-arg=-Wl,-plugin-opt,-mattr=-lsx')