use target_compile_definitions (#1440)

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3961f81..585cec6 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -32,7 +32,7 @@
 # libpfm, if available
 if (HAVE_LIBPFM)
   target_link_libraries(benchmark PRIVATE pfm)
-  add_definitions(-DHAVE_LIBPFM)
+  target_compile_definitions(benchmark PRIVATE -DHAVE_LIBPFM)
 endif()
 
 # Link threads.
@@ -56,7 +56,7 @@
 endif()
 
 if (NOT BUILD_SHARED_LIBS)
-  add_definitions(-DBENCHMARK_STATIC_DEFINE)
+  target_compile_definitions(benchmark PRIVATE -DBENCHMARK_STATIC_DEFINE)
 endif()
 
 # Benchmark main library