cmake: refactor check_prototype_definition

Introduce `check_prototype_definition_safe` that is safe for `Werror`
usage.

CMakeLists.txt

@@ -94,7 +94,7 @@ include(CheckLibraryExists)
 include(CheckFunctionExists)
 include(CheckSymbolExists)
 include(CheckStructHasMember)
-include(CheckPrototypeDefinition)
+include(CheckPrototypeDefinitionSafe)
 include(AddCFlagIfSupported)
 include(FindPkgLibraries)
 include(FindThreads)

cmake/CheckPrototypeDefinitionSafe.cmake

@@ -0,0 +1,16 @@
+include(CheckPrototypeDefinition)
+
+function(check_prototype_definition_safe function prototype return header variable)
+	# temporarily save CMAKE_C_FLAGS and disable warnings about unused
+	# unused functions and parameters, otherwise they will always fail
+	# if ENABLE_WERROR is on
+	set(SAVED_CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
+
+	disable_warnings(unused-function)
+	disable_warnings(unused-parameter)
+
+	check_prototype_definition("${function}" "${prototype}" "${return}" "${header}" "${variable}")
+
+	# restore CMAKE_C_FLAGS
+	set(CMAKE_C_FLAGS "${SAVED_CMAKE_C_FLAGS}")
+endfunction()

src/CMakeLists.txt

@@ -58,40 +58,30 @@ add_feature_info(futimens GIT_USE_FUTIMENS "futimens support")
 
 # qsort
 
-# for these tests, temporarily save CMAKE_C_FLAGS and disable warnings about
-# unused functions and parameters, otherwise they will always fail if
-# ENABLE_WERROR is on
-set(SAVED_CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
-disable_warnings(unused-function)
-disable_warnings(unused-parameter)
-
 # old-style FreeBSD qsort_r() has the 'context' parameter as the first argument
 # of the comparison function:
-check_prototype_definition(qsort_r
+check_prototype_definition_safe(qsort_r
 	"void (qsort_r)(void *base, size_t nmemb, size_t size, void *context, int (*compar)(void *, const void *, const void *))"
 	"" "stdlib.h" GIT_QSORT_BSD)
 
 # GNU or POSIX qsort_r() has the 'context' parameter as the last argument of the
 # comparison function:
-check_prototype_definition(qsort_r
+check_prototype_definition_safe(qsort_r
 	"void (qsort_r)(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *, void *), void *context)"
 	"" "stdlib.h" GIT_QSORT_GNU)
 
 # C11 qsort_s() has the 'context' parameter as the last argument of the
 # comparison function, and returns an error status:
-check_prototype_definition(qsort_s
+check_prototype_definition_safe(qsort_s
 	"errno_t (qsort_s)(void *base, rsize_t nmemb, rsize_t size, int (*compar)(const void *, const void *, void *), void *context)"
 	"0" "stdlib.h" GIT_QSORT_C11)
 
 # MSC qsort_s() has the 'context' parameter as the first argument of the
 # comparison function, and as the last argument of qsort_s():
-check_prototype_definition(qsort_s
+check_prototype_definition_safe(qsort_s
 	"void (qsort_s)(void *base, size_t num, size_t width, int (*compare )(void *, const void *, const void *), void *context)"
 	"" "stdlib.h" GIT_QSORT_MSC)
 
-# restore CMAKE_C_FLAGS
-set(CMAKE_C_FLAGS "${SAVED_CMAKE_C_FLAGS}")
-
 # random / entropy data
 
 check_function_exists(getentropy GIT_RAND_GETENTROPY)