Bug 1604814 - change the OS X SDK headers check to only run on OS X; r=rstewart

The doubling of `when` is needed: the `try_run` when ensures that we
only execute the compiler on OS X, and the `@depends` when ensures that
we don't look at the `None` result (which would normally indicate
failure) on non-OS X hosts.

Differential Revision: https://phabricator.services.mozilla.com/D57636

--HG--
extra : moz-landing-system : lando

build/moz.configure/toolchain.configure

@@ -1180,13 +1180,21 @@ include('compile-checks.configure')
 include('arm.configure', when=depends(target.cpu)(lambda cpu: cpu == 'arm'))
 
 
-@depends(host,
-         host_os_kernel_major_version,
-         target,
-         cxx_compiler.try_run(header='#include_next <inttypes.h>'))
-def check_have_mac_10_14_sdk(host, version, target, value):
+@depends(host, host_os_kernel_major_version, target)
+def needs_macos_sdk_headers_check(host, version, target):
     # Only an issue on Mac OS X 10.14 (and probably above).
-    if host.kernel != 'Darwin' or target.kernel !='Darwin' or version < '18' or value:
+    if host.kernel != 'Darwin' or target.kernel !='Darwin' or version < '18':
+        return
+
+    return True
+
+
+@depends(cxx_compiler.try_run(header='#include_next <inttypes.h>',
+                              check_msg='for macOS SDK headers',
+                              when=needs_macos_sdk_headers_check),
+         when=needs_macos_sdk_headers_check)
+def check_have_mac_10_14_sdk(value):
+    if value:
         return
 
     die('System inttypes.h not found. Please try running '