silence macos warning

[timblechmann]

i was running into this compiler invocation error on two different macos computers. the error seems harmless, but nevertheless it's ugly and confuses devs.

i don't exactly like the fix of adding an implicit preprocessor path, but otoh the change is not very intrusive. thoughts?

---

on macos we are running into the following warning when trying to run
the system autodetection:

/Applications/Xcode11.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string.h:61:15:
fatal error: 'string.h' file not
      found
              ^~~~~~~~~~

it seems that the compiler cannot find the sdk root, so the c++ headers
cannot find the c headers. we therefore add the macos sdk path manually

[CLAassistant]

All committers have signed the CLA.

[czoido]

Hi @timblechmann,
Sorry for the late response.
Have you tried to set: export SDKROOT=$(xcodebuild -version -sdk macosx Path) (See: #159 (comment))
Please check if that solves your issue.

[czoido]

Related to: #159

[timblechmann]

@czoido observations:

• the warning does not seem to trigger with xcode-11.6 (i had been using this patch locally for months). it does trigger for xcode-10 though (and in the past it was triggered for 11.2)
• running the echo | clang pipeline from terminal neither shows the error on either of these compilers (which is funny)
• setting the SDKROOT environment variable seems to work around it (though i'd appreciate if i wouldn't need to do it manually)

[czoido]

Hi @timblechmann we have added this: #226 to the 0.16 milestone and that will also address this error. I'll close this one. Please check if that solves the issue, otherwise please feel free to reopen.
Thanks a lot