Issue Description:

As reported in https://forums.swift.org/t/getting-the-following-error-when-importing-darwin-or-foundation-in-swift/55619/3

I get the following error when I try to import Foundation or anything else.

Welcome to Swift version 5.5.2-dev.
Type :help for assistance.
1> import Foundation
:5:9: note: in file included from :5::5:
#import "copyfile.h"
^

error: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/copyfile.h:41:9: error: unknown type name 'uint32_t'
typedef uint32_t copyfile_flags_t;
^

:5:9: note: in file included from :5::5:
#import "copyfile.h"
^

error: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/copyfile.h:62:44: error: unknown type name 'uint32_t'
int copyfile_state_get(copyfile_state_t s, uint32_t flag, void * dst);
^

:5:9: note: in file included from :5::5:
#import "copyfile.h"
^

error: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/copyfile.h:63:44: error: unknown type name 'uint32_t'
int copyfile_state_set(copyfile_state_t s, uint32_t flag, const void * src);
^

:30:9: note: in file included from :30::30:
#import"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/clang/include/tgmath.h"
^

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/clang/include/tgmath.h:13:10: note: in file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/clang/include/tgmath.h:13:/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/clang/include/tgmath.h:13:
#include <math.h>
^

/usr/local/include/math.h:29:12: note: in file included from /usr/local/include/math.h:29:/usr/local/include/math.h:29:

...^

Seems that it is picking up header files from /usr/local/include possibly created by some other program.

I fixed it by moving /usr/local/include but I suspect I shouldn't have to.

Perhaps Swift ignores /usr/local/include in the future?