PostgreSQL does not compile on macOS SDK 15.0

Xcode 16 beta was released on 2024-06-10 and ships with macOS SDK 15.0
[1]. It appears PostgreSQL does not compile due to typedef redefiniton
errors in the regex library:

/tmp/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
-Wall -Wmissing-prototypes -Wpointer-arith
-Wdeclaration-after-statement -Werror=vla
-Werror=unguarded-availability-new -Wendif-labels
-Wmissing-format-attribute -Wcast-function-type -Wformat-security
-fno-strict-aliasing -fwrapv -fexcess-precision=standard
-Wno-unused-command-line-argument -Wno-compound-token-split-by-macro
-Wno-cast-function-type-strict -O2 -I../../../src/include -isysroot
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk
-c -o regcomp.o regcomp.c
In file included from regcomp.c:2647:
In file included from ./regc_pg_locale.c:21:
In file included from ../../../src/include/utils/pg_locale.h:16:
In file included from
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/xlocale.h:45:
In file included from
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/xlocale/_regex.h:27:
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/_regex.h:107:24:
error: typedef redefinition with different types ('__darwin_off_t'
(aka 'long long') vs 'long')
107 | typedef __darwin_off_t regoff_t;
| ^
../../../src/include/regex/regex.h:48:14: note: previous definition is here
48 | typedef long regoff_t;
| ^
In file included from regcomp.c:2647:
In file included from ./regc_pg_locale.c:21:
In file included from ../../../src/include/utils/pg_locale.h:16:
In file included from
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/xlocale.h:45:
In file included from
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/xlocale/_regex.h:27:
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/_regex.h:114:3:
error: typedef redefinition with different types ('struct regex_t' vs
'struct regex_t')
114 | } regex_t;
| ^
../../../src/include/regex/regex.h:82:3: note: previous definition is here
82 | } regex_t;
| ^
In file included from regcomp.c:2647:
In file included from ./regc_pg_locale.c:21:
In file included from ../../../src/include/utils/pg_locale.h:16:
In file included from
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/xlocale.h:45:
In file included from
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/xlocale/_regex.h:27:
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/_regex.h:119:3:
error: typedef redefinition with different types ('struct regmatch_t'
vs 'struct regmatch_t')
119 | } regmatch_t;
| ^
../../../src/include/regex/regex.h:89:3: note: previous definition is here
89 | } regmatch_t;
| ^
3 errors generated.
make[3]: *** [regcomp.o] Error 1
make[2]: *** [regex-recursive] Error 2
make[1]: *** [all-backend-recurse] Error 2
make: *** [all-src-recurse] Error 2

I've reproduced this issue by:

1. Download the XCode 16 beta 2 ZIP file:
https://developer.apple.com/services-account/download?path=/Developer_Tools/Xcode_16_beta/Xcode_16_beta.xip
2. Extract this to `/tmp`.
3. Then I ran:

export PATH=/tmp/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin:$PATH
export SDKROOT=/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk
export XCODE_DIR=/tmp/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain
export CC="$XCODE_DIR/usr/bin/clang" export CXX="$XCODE_DIR/usr/bin/clang++"

./configure CC="$CC" CXX="$CXX"
make

The compilation goes through if I comment out the "#include
<xlocale/_regex.h>" from
/tmp/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/include/xlocale.h.
However, even on macOS SDK 14.5 I see that include statement. I'm
still trying to figure out what changed here.

[1] - https://developer.apple.com/macos/