libc: Update macOS headers to SDK 26.1

[linusg]

https://developer.apple.com/documentation/xcode-release-notes/xcode-26_1-release-notes

[linusg]

Confirmed bdwgc builds now with:

--- a/build.zig
+++ b/build.zig
@@ -465,15 +465,6 @@ pub fn build(b: *std.Build) void {
         flags.append(b.allocator, "-D HAVE_DLADDR") catch unreachable;
     }
 
-    // TODO: as of zig 0.14, exception.h and getsect.h are not provided
-    // by zig itself for Darwin target.
-    if (t.os.tag.isDarwin() and !target.query.isNative()) {
-        flags.append(b.allocator,
-                     "-D MISSING_MACH_O_GETSECT_H") catch unreachable;
-        flags.append(b.allocator,
-                     "-D NO_MPROTECT_VDB") catch unreachable;
-    }
-
     if (enable_cplusplus and enable_werror) {
         if (linkage == .dynamic and t.os.tag == .windows or t.abi == .msvc) {
             // Avoid "replacement operator new[] cannot be declared inline"

[alexrp]

Oops, didn't mean to bypass CI... well, fingers crossed: https://github.com/ziglang/zig/actions/runs/19084172529