[Libomptarget] Build plugins-nextgen/common/PluginInterface with prot…

…ected visibility

Summary:
This commit sets the default visibility of PluginInterface's symbols (in
nextgen plugins) as protected. This prevents symbols from a plugin
library to be preempted by another plugin library's symbol. It applies
the same fix introduced by D136365.

Issue reported by @ggeorgakoudis.

Differential Revision: https://reviews.llvm.org/D138002

openmp/libomptarget/plugins-nextgen/common/PluginInterface/CMakeLists.txt

@@ -19,7 +19,9 @@ add_definitions("-DTARGET_NAME=PluginInterface")
 # Define the DEBUG_PREFIX.
 add_definitions(-DDEBUG_PREFIX="PluginInterface")
 
-set_property(TARGET PluginInterface PROPERTY POSITION_INDEPENDENT_CODE ON)
+set_target_properties(PluginInterface PROPERTIES
+  POSITION_INDEPENDENT_CODE ON
+  CXX_VISIBILITY_PRESET protected)
 llvm_update_compile_flags(PluginInterface)
 set(LINK_LLVM_LIBS LLVMSupport)
 if (LLVM_LINK_LLVM_DYLIB)