Fix the llvm version

Author: fzou1

.travis.yml

@@ -16,7 +16,7 @@ branches:
 
 env:
   global:
-    - LLVM_VERSION=12
+    - LLVM_VERSION=11
   matrix:
     - BUILD_TYPE=Release
     - BUILD_TYPE=Debug

CMakeLists.txt

@@ -20,7 +20,7 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     add_definitions(-DUSE_PREBUILT_LLVM)
 
     if(NOT PREFERRED_LLVM_VERSION)
-        set(PREFERRED_LLVM_VERSION "12.0.0")
+        set(PREFERRED_LLVM_VERSION "11.0.0")
     endif(NOT PREFERRED_LLVM_VERSION)
     message(STATUS "Looking for LLVM version ${PREFERRED_LLVM_VERSION}")
     find_package(LLVM ${PREFERRED_LLVM_VERSION} REQUIRED)