[LLVM][Cygwin] Enable dynamic linking of libLLVM (#146440)

These changes allow to link everything to shared LLVM library with
MSYS2 "Cygwin" toolchain.

llvm/cmake/modules/AddLLVM.cmake

@@ -137,7 +137,7 @@ function(add_llvm_symbol_exports target_name export_file)
       set_property(TARGET ${target_name} APPEND_STRING PROPERTY
                    LINK_FLAGS "  -Wl,--version-script,\"${CMAKE_CURRENT_BINARY_DIR}/${native_export_file}\"")
     endif()
-  elseif(WIN32)
+  elseif(WIN32 OR CYGWIN)
     set(native_export_file "${target_name}.def")
 
     add_custom_command(OUTPUT ${native_export_file}
@@ -153,7 +153,7 @@ function(add_llvm_symbol_exports target_name export_file)
     elseif(CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")
       # clang in msvc mode, calling a link.exe/lld-link style linker
       set(export_file_linker_flag "-Wl,/DEF:${export_file_linker_flag}")
-    elseif(MINGW)
+    elseif(MINGW OR CYGWIN)
       # ${export_file_linker_flag}, which is the plain file name, works as is
       # when passed to the compiler driver, which then passes it on to the
       # linker as an input file.
@@ -666,7 +666,7 @@ function(llvm_add_library name)
     # When building shared objects for each target there are some internal APIs
     # that are used across shared objects which we can't hide.
     if (LLVM_BUILD_LLVM_DYLIB_VIS AND NOT BUILD_SHARED_LIBS AND NOT APPLE AND
-        (NOT (WIN32 OR CYGWIN) OR (MINGW AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
+        (NOT (WIN32 OR CYGWIN) OR ((MINGW OR CYGWIN) AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
         NOT (${CMAKE_SYSTEM_NAME} MATCHES "AIX") AND
         NOT DEFINED CMAKE_CXX_VISIBILITY_PRESET)
 

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -465,7 +465,7 @@ if( LLVM_ENABLE_PIC )
 endif()
 
 if((NOT (${CMAKE_SYSTEM_NAME} MATCHES "AIX")) AND
-   (NOT (WIN32 OR CYGWIN) OR (MINGW AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")))
+   (NOT (WIN32 OR CYGWIN) OR ((MINGW OR CYGWIN) AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")))
   # GCC for MinGW does nothing about -fvisibility-inlines-hidden, but warns
   # about use of the attributes. As long as we don't use the attributes (to
   # override the default) we shouldn't set the command line options either.

llvm/include/llvm/Support/Compiler.h

@@ -133,7 +133,7 @@
 #endif
 
 #if (!(defined(_WIN32) || defined(__CYGWIN__)) ||                              \
-     (defined(__MINGW32__) && defined(__clang__)))
+     ((defined(__MINGW32__) || defined(__CYGWIN__)) && defined(__clang__)))
 #define LLVM_LIBRARY_VISIBILITY LLVM_ATTRIBUTE_VISIBILITY_HIDDEN
 // Clang compilers older then 15 do not support gnu style attributes on
 // namespaces.

llvm/lib/Target/CMakeLists.txt

@@ -22,7 +22,7 @@ add_llvm_component_library(LLVMTarget
 # When building shared objects for each target there are some internal APIs
 # that are used across shared objects which we can't hide.
 if (NOT BUILD_SHARED_LIBS AND NOT APPLE AND
-    (NOT (WIN32 OR CYGWIN) OR (MINGW AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
+    (NOT (WIN32 OR CYGWIN) OR ((MINGW OR CYGWIN) AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
     NOT (${CMAKE_SYSTEM_NAME} MATCHES "AIX") AND
     NOT DEFINED CMAKE_CXX_VISIBILITY_PRESET)
   # Set default visibility to hidden, so we don't export all the Target classes