[libipt] Do not add pt_cpuid.c if host target is arm

Otherwise, we transitively include this x86-only header
prebuilt/third_party/clang/linux-arm64/lib/clang/15.0.0/include/cpuid.h
on host arm.

Bug: 103083
Change-Id: I6d55c4b902af5d56023528b5341d0099a42958fd
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/processor-trace/+/692769
Reviewed-by: Roland McGrath <mcgrathr@google.com>

libipt/BUILD.gn

diff --git a/libipt/BUILD.gn b/libipt/BUILD.gn
index eb3fe1c..e37b532 100644
--- a/libipt/BUILD.gn
+++ b/libipt/BUILD.gn
@@ -76,7 +76,7 @@
     "src/pt_version.c",
   ]
 
-  if (is_linux || is_mac) {
+  if ((is_linux || is_mac) && host_cpu == "x64") {
     sources += [
       "internal/include/posix/pt_section_posix.h",