shims/super/cc: handle double dash in args

[alebcay]

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The cc shim currently does not handle invocations where -- is passed as an argument, which (conventionally) indicates that all following arguments be treated as positional (non-optional) arguments. As a result, any refurbished args may get appended after the -- where they are erroneously treated as input file paths:

clang: error: no such file or directory: '-isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk'
clang: error: no such file or directory: '--sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk'; did you mean '--sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk'?
clang: error: no such file or directory: '-isystem/opt/homebrew/include'
clang: error: no such file or directory: '-isystem/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers'
clang: error: no such file or directory: '-L/opt/homebrew/lib'
clang: error: no such file or directory: '-L/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Libraries'
clang: error: no such file or directory: '-Wl,-headerpad_max_install_names'

This kind of error was encountered in the wild in some core PRs, e.g. Homebrew/homebrew-core#203929, Homebrew/homebrew-core#203934, Homebrew/homebrew-core#203932, Homebrew/homebrew-core#203944.

This pull request ensures that any modifications to the arguments are applied before the -- (if -- is present).

Before:

clang called with: -- test.c
superenv added:    -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk --sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk -isystem/opt/homebrew/include -isystem/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers -L/opt/homebrew/lib -L/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Libraries -Wl,-headerpad_max_install_names
superenv executed: clang -- test.c -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk --sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk -isystem/opt/homebrew/include -isystem/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers -L/opt/homebrew/lib -L/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Libraries -Wl,-headerpad_max_install_names

After:

clang called with: -- test.c
superenv added:    -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk --sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk -isystem/opt/homebrew/include -isystem/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers -L/opt/homebrew/lib -L/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Libraries -Wl,-headerpad_max_install_names
superenv executed: clang -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk --sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk -isystem/opt/homebrew/include -isystem/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers -L/opt/homebrew/lib -L/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/Libraries -Wl,-headerpad_max_install_names -- test.c

[carlocab]

Thanks; nice work!

[MikeMcQuaid]

Good catch, thanks!