compiler-rt: export __aeabi_read_tp for arm-freebsd

FreeBSD normally provides this symbol in libc, but it's in the
FBSDprivate_1.0 namespace, so it doesn't get included in our abilists file.
Fortunately, the implementation is identical for Linux and FreeBSD, so we can
just provide it in compiler-rt.

It's interesting to note that the same is not true for NetBSD where the
implementation is more complex to support older Arm versions. But we do include
the symbol in our abilists file for NetBSD libc, so that's fine.

closes ziglang#25215

Author: alexrp

lib/compiler_rt/arm.zig

@@ -37,7 +37,7 @@ comptime {
             @export(&__aeabi_memclr4, .{ .name = "__aeabi_memclr4", .linkage = common.linkage, .visibility = common.visibility });
             @export(&__aeabi_memclr8, .{ .name = "__aeabi_memclr8", .linkage = common.linkage, .visibility = common.visibility });
 
-            if (builtin.os.tag == .linux) {
+            if (builtin.os.tag == .linux or builtin.os.tag == .freebsd) {
                 @export(&__aeabi_read_tp, .{ .name = "__aeabi_read_tp", .linkage = common.linkage, .visibility = common.visibility });
             }