[evolution] SetupBuildFlags.cmake: Use -Werror=implicit-function-declaration only for C code compilation

[Milan Crha <mcrha src gnome org>]

commit 1624857fc5eb25272f64626220ae861f3d5211bc
Author: Milan Crha <mcrha redhat com>
Date:   Wed May 13 09:20:22 2020 +0200

    SetupBuildFlags.cmake: Use -Werror=implicit-function-declaration only for C code compilation
    
    The C++ code produces a compile time warning:
      cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
    despite CMake's check_cxx_compiler_flag() returning success.

 cmake/modules/SetupBuildFlags.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/cmake/modules/SetupBuildFlags.cmake b/cmake/modules/SetupBuildFlags.cmake
index 6e936df5f3..d5ce5f3c5e 100644
--- a/cmake/modules/SetupBuildFlags.cmake
+++ b/cmake/modules/SetupBuildFlags.cmake
@@ -10,7 +10,6 @@ endif(CMAKE_CXX_COMPILER_ID)
 
 macro(setup_build_flags _maintainer_mode)
        list(APPEND proposed_flags
-               -Werror-implicit-function-declaration
                -Wformat
                -Wformat-security
                -Winit-self
@@ -40,6 +39,7 @@ macro(setup_build_flags _maintainer_mode)
 
        list(APPEND proposed_c_flags
                ${proposed_flags}
+               -Werror-implicit-function-declaration
                -Wdeclaration-after-statement
                -Wno-missing-field-initializers
                -Wno-sign-compare