RFR: [9] 8043340 & 8043591: [macosx] Build system issues

[David DeHaven]

Will README-builds.html be updated as part of the compiler update? It (will be) outdated.

I don't think it needs to be part of this patch since I'd like to backport this (and the other patches I've contributed recently) to 8u after it incubates for a while.

-DrD-

>> Only thing I can think of now is that some of the error/warning messages do not start with a capital letter. Looks good and nice work!
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> I'll fix those before pushing.
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>>> I also removed using SDKROOT from the env, since we ignore the environment. Only two args affect SYSROOT now, --with-sysroot and --with-sdk-name.
>> I think that's good too, I had some doubts about that. Is that environment variable set by the system in some way or is it something one sets manually? If it's something the system sets, then perhaps it's worth looking at (compare VS100COMNTOOLS on windows which points to visual studio). But since we can get the information from xcodebuild anyway, it really doesn't matter.
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> Right. SDKROOT is set when Xcode is building, so it would either be set by the user or if someone were building OpenJDK as part of an Xcode project.
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>> Nice to see a speedup in building too. The broken case seems ok to me. Not much we can do there. Silently switching to clang would be bad too.
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> Agreed!
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> -DrD-
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