[clang] Disable gch-probe.c on AIX as -gmodules is not supported there yet. (#78513)

Followup fix for #77711

Author: Bigcheese

clang/test/PCH/gch-probe.c

@@ -1,3 +1,7 @@
+// Unsupported on AIX because we don't support the requisite "__clangast"
+// section in XCOFF yet.
+// UNSUPPORTED: target={{.*}}-aix{{.*}}
+
 // For GCC compatibility, clang should probe also with the .gch extension.
 // RUN: %clang -x c-header -c %s -o %t.h.gch
 // RUN: %clang -fsyntax-only -include %t.h %s