Use more explicit architecture compiler options on Linux

[aaronfranke]

This PR takes a piece out of #55778. Specifically, this PR was driven by this review comment from @akien-mga:

I tested this PR on x86_64, arm64, and rv64 hosts & targets, and compiling x86_32 on x86_64.

[akien-mga]

You seem to have missed some cross-compilation code further down that does some of this already, which should likely be removed. The hardcoded lib folder path are actually bogus on many distros, but shouldn't be needed(?).

diff --git a/platform/linuxbsd/detect.py b/platform/linuxbsd/detect.py
index 72bffceb1f..02d8d20fbf 100644
--- a/platform/linuxbsd/detect.py
+++ b/platform/linuxbsd/detect.py
@@ -469,16 +469,6 @@ def configure(env: "Environment"):
     if platform.system() == "FreeBSD":
         env.Append(LINKFLAGS=["-lkvm"])
 
-    ## Cross-compilation
-    # TODO: Support cross-compilation on architectures other than x86.
-    host_is_64_bit = sys.maxsize > 2**32
-    if host_is_64_bit and env["arch"] == "x86_32":
-        env.Append(CCFLAGS=["-m32"])
-        env.Append(LINKFLAGS=["-m32", "-L/usr/lib/i386-linux-gnu"])
-    elif not host_is_64_bit and env["arch"] == "x86_64":
-        env.Append(CCFLAGS=["-m64"])
-        env.Append(LINKFLAGS=["-m64", "-L/usr/lib/i686-linux-gnu"])
-
     # Link those statically for portability
     if env["use_static_cpp"]:
         env.Append(LINKFLAGS=["-static-libgcc", "-static-libstdc++"])

Edit: I'm moving this up in #84307 which will conflict with this PR, but it's a safe-ish fixup for 4.2. You can rebase and remove that whole block as yours supersedes it fully.

[akien-mga]

Are both -m64/-m32 and -march needed at the same time, or does the latter make the old -m64 and -m32 flags redundant?

[aaronfranke]

They are both required, yes.

If you try to use -march= on x86 without the proper bitness or specifying -m32/-m64 it will not work.

While confusing, -m32/-m64 specifically refers to x86_32 and x86_64, not 32-bit and 64-bit in general.