diff -Naur libilbc-3.0.4.old/CMakeLists.txt libilbc-3.0.4/CMakeLists.txt
--- libilbc-3.0.4.old/CMakeLists.txt	2022-05-25 10:51:43.530630048 +0200
+++ libilbc-3.0.4/CMakeLists.txt	2022-05-25 10:52:59.434028167 +0200
@@ -52,15 +52,11 @@
 
 if((CMAKE_C_COMPILER_ID STREQUAL "GNU") OR
    (CMAKE_C_COMPILER_ID MATCHES "Clang" AND CMAKE_C_COMPILER_FRONTEND_VARIANT STREQUAL "GNU"))
-    set(CMAKE_C_FLAGS "-Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wno-unused-parameter -fno-strict-aliasing")
-    set(CMAKE_C_FLAGS_DEBUG "-g")
-    set(CMAKE_C_FLAGS_RELEASE "-O2")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
 endif()
 if((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") OR
    (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "GNU"))
-    set(CMAKE_CXX_FLAGS "-Wall -Wextra -Wno-unused-parameter -fno-strict-aliasing")
-    set(CMAKE_CXX_FLAGS_DEBUG "-g")
-    set(CMAKE_CXX_FLAGS_RELEASE "-O2")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 endif()
 
 if(CMAKE_C_COMPILER_ID STREQUAL "MSVC")