update cmake, update readme, in response to the dynamic linking fiasco

Author: andrewrk

README.md

@@ -58,10 +58,16 @@ brew install cmake llvm
 brew outdated llvm || brew upgrade llvm
 mkdir build
 cd build
-cmake .. -DCMAKE_PREFIX_PATH=$(brew --prefix llvm) -DZIG_PREFER_CLANG_CPP_DYLIB=ON
+cmake .. -DCMAKE_PREFIX_PATH=$(brew --prefix llvm)
 make install
 ```
 
+You will now run into this issue:
+[homebrew and llvm 10 packages in apt.llvm.org are broken with undefined reference to getPollyPluginInfo](https://github.com/ziglang/zig/issues/4799)
+
+Please help upstream LLVM and Homebrew solve this issue, there is nothing Zig
+can do about it. See that issue for a workaround you can do in the meantime.
+
 ##### Windows
 
 See https://github.com/ziglang/zig/wiki/Building-Zig-on-Windows

cmake/Findclang.cmake

@@ -18,7 +18,7 @@ find_path(CLANG_INCLUDE_DIRS NAMES clang/Frontend/ASTUnit.h
 )
 
 if(ZIG_PREFER_CLANG_CPP_DYLIB)
-  find_library(CLANG_CPP_DYLIB
+  find_library(CLANG_LIBRARIES
     NAMES
       clang-cpp-10.0
       clang-cpp100
@@ -31,9 +31,7 @@ if(ZIG_PREFER_CLANG_CPP_DYLIB)
   )
 endif()
 
-if(CLANG_CPP_DYLIB)
-  set(CLANG_LIBRARIES ${CLANG_CPP_DYLIB})
-else()
+if(NOT CLANG_LIBRARIES)
   macro(FIND_AND_ADD_CLANG_LIB _libname_)
     string(TOUPPER ${_libname_} _prettylibname_)
     find_library(CLANG_${_prettylibname_}_LIB NAMES ${_libname_}