More portable PIC (#966)

Author: lemire

src/CMakeLists.txt

@@ -11,7 +11,10 @@ add_library(ada ada.cpp)
 target_compile_features(ada PUBLIC cxx_std_20)
 target_include_directories(ada PRIVATE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}> )
 target_include_directories(ada PUBLIC "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>")
-
+if(NOT DEFINED CMAKE_POSITION_INDEPENDENT_CODE)
+  # We default to ON for all targets, so that we can use the library in shared libraries.
+  set_target_properties(ada PROPERTIES POSITION_INDEPENDENT_CODE ON)
+endif(NOT DEFINED CMAKE_POSITION_INDEPENDENT_CODE)
 if(MSVC)
   if("${MSVC_TOOLSET_VERSION}" STREQUAL "140")
     target_compile_options(ada INTERFACE /W0 /sdl)
@@ -20,9 +23,6 @@ if(MSVC)
     target_compile_options(ada PRIVATE /WX /W3 /sdl /w34714) # https://docs.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-4-c4714?view=vs-2019
   endif()
 else(MSVC)
-  if(NOT WIN32)
-    target_compile_options(ada INTERFACE -fPIC)
-  endif()
   message(STATUS "Assuming GCC-like compiler.")
   target_compile_options(ada PRIVATE -Wall -Wextra -Weffc++)
   if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")