[Driver][FreeBSD] Generalise lib32 handling to support arm

The current code maintains its own list of 32-bit architectures for
which there is a 64-bit FreeBSD architecture that supports it for lib32.
This is unnecessary (if it's not supported, the directory just won't
exist), and means that, when FreeBSD gains lib32 support for a new
architecture, you need an updated toolchain that knows about it.
Instead we can check for any 32-bit architecture and have forwards
compatibility.

This is motivated by FreeBSD adding support for building arm lib32
libraries on aarch64.

Co-authored-by: Mike Karels <karels@FreeBSD.org>

clang/lib/Driver/ToolChains/FreeBSD.cpp

@@ -376,8 +376,7 @@ FreeBSD::FreeBSD(const Driver &D, const llvm::Triple &Triple,
 
   // When targeting 32-bit platforms, look for '/usr/lib32/crt1.o' and fall
   // back to '/usr/lib' if it doesn't exist.
-  if ((Triple.getArch() == llvm::Triple::x86 || Triple.isMIPS32() ||
-       Triple.isPPC32()) &&
+  if (Triple.isArch32Bit() &&
       D.getVFS().exists(concat(getDriver().SysRoot, "/usr/lib32/crt1.o")))
     getFilePaths().push_back(concat(getDriver().SysRoot, "/usr/lib32"));
   else