Get back -Wsigned-one-bit-field and fix sources according to it

Signed-off-by: makise-homura <akemi_homura@kurisa.ch>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index d2cf446..8833246 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -175,10 +175,6 @@
             set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wformat-signedness")
         endif()
     endif()
-    CHECK_C_COMPILER_FLAG("-Wno-signed-one-bit-field" C_COMPILER_SUPPORTS_WSIGNED_ONE_BIT_FIELD)
-    if(C_COMPILER_SUPPORTS_WSIGNED_ONE_BIT_FIELD)
-        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-signed-one-bit-field")
-    endif()
     set(CMAKE_C_FLAGS_RELEASE     "-O2")
     set(CMAKE_C_FLAGS_DEBUG       "-O0 -g3")
     set(CMAKE_C_FLAGS_COVERAGE    "-O0 -g3 --coverage")
diff --git a/tests/include/test/macros.h b/tests/include/test/macros.h
index aaf13ad..21552e7 100644
--- a/tests/include/test/macros.h
+++ b/tests/include/test/macros.h
@@ -75,7 +75,7 @@
 /* A compile-time constant with the value 0. If `const_expr` is not a
  * compile-time constant with a nonzero value, cause a compile-time error. */
 #define STATIC_ASSERT_EXPR( const_expr )                                \
-    ( 0 && sizeof( struct { int STATIC_ASSERT : 1 - 2 * ! ( const_expr ); } ) )
+    ( 0 && sizeof( struct { unsigned int STATIC_ASSERT : 1 - 2 * ! ( const_expr ); } ) )
 /* Return the scalar value `value` (possibly promoted). This is a compile-time
  * constant if `value` is. `condition` must be a compile-time constant.
  * If `condition` is false, arrange to cause a compile-time error. */