Remove PSTL from the top-level monorepo (llvm#143717)

The RFC for this removal can be found at:
https://discourse.llvm.org/t/rfc-removing-pstl/86807

Note, libc++ still supports PSTL. That support is integrated directly
into the libc++ source tree.

There is no release note for this removal because it's not really clear
that this was user-facing facilities or where such a release note should
live.

Author: AaronBallman

llvm/CMakeLists.txt

@@ -109,7 +109,7 @@ endif()
 # This allows an easy way of setting up a build directory for llvm and another
 # one for llvm+clang+... using the same sources.
 # These projects will be included when "all" is included in LLVM_ENABLE_PROJECTS.
-set(LLVM_ALL_PROJECTS "bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libclc;lld;lldb;mlir;openmp;polly;pstl")
+set(LLVM_ALL_PROJECTS "bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libclc;lld;lldb;mlir;openmp;polly")
 if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
   # Disallow 'openmp' as a LLVM PROJECT on AIX as the supported way is to use
   # LLVM_ENABLE_RUNTIMES.
@@ -141,7 +141,7 @@ endforeach()
 # As we migrate runtimes to using the bootstrapping build, the set of default runtimes
 # should grow as we remove those runtimes from LLVM_ENABLE_PROJECTS above.
 set(LLVM_DEFAULT_RUNTIMES "libcxx;libcxxabi;libunwind")
-set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload;flang-rt;libclc")
+set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;libcxx;compiler-rt;openmp;llvm-libgcc;offload;flang-rt;libclc")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all")

llvm/docs/CMake.rst

@@ -588,7 +588,7 @@ enabled sub-projects. Nearly all of these variable names begin with
 
   The full list is:
 
-  ``bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libc;libclc;lld;lldb;mlir;openmp;polly;pstl``
+  ``bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libc;libclc;lld;lldb;mlir;openmp;polly``
 
   .. note::
     Some projects listed here can also go in ``LLVM_ENABLE_RUNTIMES``. They
@@ -610,7 +610,7 @@ enabled sub-projects. Nearly all of these variable names begin with
 
   The full list is:
 
-  ``libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload``
+  ``libc;libunwind;libcxxabi;libcxx;compiler-rt;openmp;llvm-libgcc;offload``
 
   To enable all of them, use: