llvmPackages.libcxxabi: dedupe no-threads.patch

found with fdupes

```
pkgs/development/compilers/llvm/8/libcxxabi/no-threads.patch
pkgs/development/compilers/llvm/10/libcxxabi/no-threads.patch
pkgs/development/compilers/llvm/9/libcxxabi/no-threads.patch
pkgs/development/compilers/llvm/11/libcxxabi/no-threads.patch
```

pkgs/development/compilers/llvm/10/libcxxabi/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation {
   '';
 
   patches = [
-    ./no-threads.patch
+    ../../common/libcxxabi/no-threads.patch
     ./gnu-install-dirs.patch
   ];
 

pkgs/development/compilers/llvm/11/libcxxabi/default.nix

@@ -26,7 +26,7 @@ stdenv.mkDerivation {
   '';
 
   patches = [
-    ./no-threads.patch
+    ../../common/libcxxabi/no-threads.patch
     ./gnu-install-dirs.patch
   ];
 

pkgs/development/compilers/llvm/11/libcxxabi/no-threads.patch

@@ -1,12 +0,0 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index 4138acf..41b4763 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -362,6 +362,7 @@ if (NOT LIBCXXABI_ENABLE_THREADS)
-                         " is also set to ON.")
-   endif()
-   add_definitions(-D_LIBCXXABI_HAS_NO_THREADS)
-+  add_definitions(-D_LIBCPP_HAS_NO_THREADS)
- endif()
- 
- if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)

pkgs/development/compilers/llvm/8/libcxxabi/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation {
   '';
 
   patches = [
-    ./no-threads.patch
+    ../../common/libcxxabi/no-threads.patch
     ./gnu-install-dirs.patch
   ];
 

pkgs/development/compilers/llvm/8/libcxxabi/no-threads.patch

@@ -1,12 +0,0 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index 4138acf..41b4763 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -362,6 +362,7 @@ if (NOT LIBCXXABI_ENABLE_THREADS)
-                         " is also set to ON.")
-   endif()
-   add_definitions(-D_LIBCXXABI_HAS_NO_THREADS)
-+  add_definitions(-D_LIBCPP_HAS_NO_THREADS)
- endif()
- 
- if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)

pkgs/development/compilers/llvm/9/libcxxabi/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation {
   '';
 
   patches = [
-    ./no-threads.patch
+    ../../common/libcxxabi/no-threads.patch
     ./gnu-install-dirs.patch
   ];
 

pkgs/development/compilers/llvm/9/libcxxabi/no-threads.patch

@@ -1,12 +0,0 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index 4138acf..41b4763 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -362,6 +362,7 @@ if (NOT LIBCXXABI_ENABLE_THREADS)
-                         " is also set to ON.")
-   endif()
-   add_definitions(-D_LIBCXXABI_HAS_NO_THREADS)
-+  add_definitions(-D_LIBCPP_HAS_NO_THREADS)
- endif()
- 
- if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)