pw_build: Disable CGo on MacOS

This tells the Go compiler to build without the C standard library on
MacOS due to issues with include paths in certain environments.

Change-Id: I33cba8abeb32350af58347afc7c768cc18a31a3d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/45443
Pigweed-Auto-Submit: Alexei Frolov <frolv@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Joe Ethier <jethier@google.com>

pw_build/go.gni

diff --git a/pw_build/go.gni b/pw_build/go.gni
index 3434883..49230f2 100644
--- a/pw_build/go.gni
+++ b/pw_build/go.gni
@@ -126,6 +126,14 @@
       "GO111MODULE=off",
       "GOPATH=$_default_gopath",
     ]
+
+    if (host_os == "mac") {
+      # TODO(frolv): Some versions of Go for MacOS have issues finding the C
+      # stdlib headers. Temporarily disable CGo on Mac. The root cause of this
+      # issue should be investigated and fixed.
+      env += [ "CGO_ENABLED=0" ]
+    }
+
     args_file = _deps_metadata_file
 
     # If the args file is empty, don't run the "go get" command.
@@ -152,6 +160,14 @@
       "GO111MODULE=off",
       "GOPATH+=$_default_gopath",
     ]
+
+    if (host_os == "mac") {
+      # TODO(frolv): Some versions of Go for MacOS have issues finding the C
+      # stdlib headers. Temporarily disable CGo on Mac. The root cause of this
+      # issue should be investigated and fixed.
+      env += [ "CGO_ENABLED=0" ]
+    }
+
     env_file = _metadata_file
 
     _binary_name = get_path_info(invoker.package, "name")