[cmake] Ignore pstl in LLVM_ENABLE_PROJECTS (#146070)

This should fix the premerge-monolithic-linux bot. This can be removed
after the next build master restart.

Author: rnk

llvm/CMakeLists.txt

@@ -130,6 +130,14 @@ set(LLVM_ENABLE_PROJECTS "" CACHE STRING
 if( LLVM_ENABLE_PROJECTS STREQUAL "all" )
   set( LLVM_ENABLE_PROJECTS ${LLVM_ALL_PROJECTS})
 endif()
+
+# The pstl project was removed. Ignore it to pacify certain buildbots.
+list(FIND LLVM_ENABLE_PROJECTS "pstl" FOUND_INDEX)
+if(NOT "${FOUND_INDEX}" STREQUAL "-1")
+  message(WARNING "The pstl project has been removed and will not be built")
+  list(REMOVE_ITEM LLVM_ENABLE_PROJECTS "pstl")
+endif()
+
 foreach(proj ${LLVM_ENABLE_PROJECTS})
   if (NOT proj STREQUAL "llvm" AND NOT "${proj}" IN_LIST LLVM_KNOWN_PROJECTS)
      MESSAGE(FATAL_ERROR "${proj} isn't a known project: ${LLVM_KNOWN_PROJECTS}. Did you mean to enable it as a runtime in LLVM_ENABLE_RUNTIMES?")