[Bug 46651] New: winegcc does not accept additional flags

https://bugs.winehq.org/show_bug.cgi?id=46651

Bug ID: 46651
           Summary: winegcc does not accept additional flags
           Product: Wine
           Version: 4.1
          Hardware: x86-64
                OS: Mac OS X
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: -unknown
          Assignee: [e-mail]
          Reporter: [e-mail]

Created attachment 63573
  --> https://bugs.winehq.org/attachment.cgi?id=63573
log

As macOS 10.14 SDK does not provide 32-bit libraries anymore, one possible way
to compile wine is to get an earlier SDK and use `-isysroot` switch to make
compiler use correct SDK path. (Getting a complete Xcode and using
`xcode-select` should be possible but takes too much disk space. Stripped down
macOS SDK and toolchain could save several GBs)

However, when compiling wine, `winegcc` does not pass any flag to underlying
`cc`, so wine dlls that link to macOS frameworks won't find the correct SDK to
link to.

There is a log below which is one of the failing dll. Command line is given by
`make`. The 10.13 SDK is at
`/Users/MrX/Developer13/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk`,
and different ways trying to pass the `-isysroot` switch such as environment
variable and appending desired switch all failed.

I've tried to manually build the file using command line given by `winegcc -v`
with `-isysroot` appended and I could get the desired .so file.