Xcode 27's math.h uses the __need_infinity_nan protocol provided by
matching Clang resource headers. Zig 0.16's bundled float.h predates
that protocol, causing the bundled libc++ compilation to fail.
Overlay the SDK math.h through the Apple SDK libc include path and
provide the missing infinity and NaN definitions. The compatibility
header can be removed once Zig's bundled Clang headers support the
protocol.
