cmd/go/internal/work: allow a bunch of loong64-specific flags

cmd/go/internal/work: allow a bunch of loong64-specific flags

Recognize and allow all LoongArch-specific CFLAGS as standardized
in the LoongArch Toolchain Conventions v1.1, and implemented in current
versions of GCC and Clang, to enable advanced cgo use cases on loong64.
These flags are also allowed for linker invocations in case of possible
LTO.

See: https://github.com/loongson/la-toolchain-conventions/blob/releases/v1.1/LoongArch-toolchain-conventions-EN.adoc#list

While at it, also add support for -mtls-dialect as some C programs
may benefit performance-wise from the optional TLSDESC usage. This flag
is not specific to loong64 though; it is available for amd64, arm,
arm64, loong64, riscv64 and x86.

Fixes #71597.

Change-Id: I35d2507edb71fa324ae429a3ae3c739644a9cac1
Reviewed-on: https://go-review.googlesource.com/c/go/+/647956
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Meidan Li <limeidan@loongson.cn>