Our llvm include path is not in the include list tried by default.

--- zig-0.7.1.orig/cmake/Findllvm.cmake
+++ zig-0.7.1/cmake/Findllvm.cmake
@@ -12,6 +12,7 @@
     /usr/lib/llvm/12/include
     /usr/lib/llvm-12/include
     /usr/lib/llvm-12.0/include
+    /usr/lib/llvm12/include
     /usr/local/llvm12/include
     /usr/local/llvm120/include
     /mingw64/include