Compilation: Don't pass -mabi to Clang on powerpc64(le)-freebsd.

The driver doesn't support it, and FreeBSD 13+ on PPC64 uses ELFv2 anyway.

Author: alexrp

src/Compilation.zig

@@ -5775,7 +5775,10 @@ pub fn addCCArgs(
 
     if (target_util.llvmMachineAbi(target)) |mabi| {
         // Clang's integrated Arm assembler doesn't support `-mabi` yet...
-        if (!(target.cpu.arch.isArm() and (ext == .assembly or ext == .assembly_with_cpp))) {
+        // Clang's FreeBSD driver doesn't support `-mabi` on PPC64 (ELFv2 is used anyway).
+        if (!(target.cpu.arch.isArm() and (ext == .assembly or ext == .assembly_with_cpp)) and
+            !(target.cpu.arch.isPowerPC64() and target.os.tag == .freebsd))
+        {
             try argv.append(try std.fmt.allocPrint(arena, "-mabi={s}", .{mabi}));
         }
     }