clang 19.1.1_0+analyzer: can't find standard headers

[paul-j-lucas (Paul J. Lucas)]

I had the previous clang-19 installed and everything worked fine, but since the update, trying to compile a simple "hello, world" program results in:

$ clang-mp-19 hello.c -o hello
hello.c:1:10: fatal error: 'stdio.h' file not found
    1 | #include <stdio.h>
      |          ^~~~~~~~~
1 error generated.

The files, however, are there:

$ port contents clang-19 | grep stdio.h
  /opt/local/libexec/llvm-19/include/c++/v1/stdio.h
  /opt/local/libexec/llvm-19/lib/clang/19/include/llvm_libc_wrappers/stdio.h

Other information of likely interest:

$ system_profiler SPSoftwareDataType SPHardwareDataType
Software:

    System Software Overview:

      System Version: macOS 13.6.9 (22G830)
      Kernel Version: Darwin 22.6.0
      Boot Volume: Macintosh HD
      Boot Mode: Normal
      Computer Name: iMac
      User Name: Paul J. Lucas (pjl)
      Secure Virtual Memory: Enabled
      System Integrity Protection: Enabled
      Time since boot: 41 days, 7 hours, 49 minutes

Hardware:

    Hardware Overview:

      Model Name: iMac
      Model Identifier: iMac18,3
      Processor Name: Quad-Core Intel Core i5
      Processor Speed: 3.4 GHz
      Number of Processors: 1
      Total Number of Cores: 4
      L2 Cache (per Core): 256 KB
      L3 Cache: 6 MB
      Memory: 16 GB
      System Firmware Version: 529.140.2.0.0
      OS Loader Version: 577.140.2~22
      SMC Version (system): 2.41f2
      Serial Number (system): C02YF02SJ1GN
      Hardware UUID: 2FCAC61C-2069-55F8-95A6-058A0DAE8522
      Provisioning UDID: 2FCAC61C-2069-55F8-95A6-058A0DAE8522

$ pkgutil --pkg-info=com.apple.pkg.CLTools_Executables
package-id: com.apple.pkg.CLTools_Executables
version: 15.1.0.0.1.1700200546
volume: /
location: /
install-time: 1703338038

BTW: the previous version of the port installed binaries; this version of the port compiles from source (and it takes a really long time).