llvmPackages_15: update licenses

Context: #194634 (comment)

All the subprojects seem to be uniformly licensed under NCSA and the
LLVM license now (with the exception of openmp which has an additional
Intel license that doesn't seem to be in SPDX?); see:
 - https://github.com/llvm/llvm-project/blob/llvmorg-15.0.7/compiler-rt/LICENSE.TXT
 - https://github.com/llvm/llvm-project/blob/llvmorg-15.0.7/libcxx/LICENSE.TXT
 - https://github.com/llvm/llvm-project/blob/llvmorg-15.0.7/libcxxabi/LICENSE.TXT
 - https://github.com/llvm/llvm-project/blob/llvmorg-15.0.7/openmp/LICENSE.TXT

pkgs/development/compilers/llvm/15/compiler-rt/default.nix

@@ -152,8 +152,5 @@ stdenv.mkDerivation {
       implementations of run-time libraries for dynamic testing tools such as
       AddressSanitizer, ThreadSanitizer, MemorySanitizer, and DataFlowSanitizer.
     '';
-    # "All of the code in the compiler-rt project is dual licensed under the MIT
-    # license and the UIUC License (a BSD-like license)":
-    license = with lib.licenses; [ mit ncsa ];
   };
 }

pkgs/development/compilers/llvm/15/default.nix

@@ -35,7 +35,7 @@ let
   };
 
   llvm_meta = {
-    license     = lib.licenses.ncsa;
+    license     = with lib.licenses; [ ncsa llvm-exception ];
     maintainers = lib.teams.llvm.members;
     platforms   = lib.platforms.all;
   };

pkgs/development/compilers/llvm/15/libcxx/default.nix

@@ -103,8 +103,5 @@ stdenv.mkDerivation rec {
       libc++ is an implementation of the C++ standard library, targeting C++11,
       C++14 and above.
     '';
-    # "All of the code in libc++ is dual licensed under the MIT license and the
-    # UIUC License (a BSD-like license)":
-    license = with lib.licenses; [ mit ncsa ];
   };
 }

pkgs/development/compilers/llvm/15/libcxxabi/default.nix

@@ -100,9 +100,6 @@ stdenv.mkDerivation rec {
     longDescription = ''
       libc++abi is a new implementation of low level support for a standard C++ library.
     '';
-    # "All of the code in libc++abi is dual licensed under the MIT license and
-    # the UIUC License (a BSD-like license)":
-    license = with lib.licenses; [ mit ncsa ];
     maintainers = llvm_meta.maintainers ++ [ lib.maintainers.vlstill ];
   };
 }

pkgs/development/compilers/llvm/15/openmp/default.nix

@@ -67,8 +67,5 @@ stdenv.mkDerivation rec {
       "clang -fopenmp" must be linked before it can run and the library that
       supports offload to target devices.
     '';
-    # "All of the code is dual licensed under the MIT license and the UIUC
-    # License (a BSD-like license)":
-    license = with lib.licenses; [ mit ncsa ];
   };
 }