CMake: check if the compiler supports using precompiled headers

Build the cotire test project and check if it succeeds. Also check if the
'had text segment at different address' warning does not appear in the build
output. If it does not succeed, disable usage of precompiled headers.

If the PCH option was changed, clean the project and rebuild it again. Do not
clean everytime the project is configured because (re)building the cotire test
project takes some time.

build/cmake/modules/cotire_test/src/CMakeLists.txt

@@ -0,0 +1,31 @@
+# cotire example project
+
+add_executable(example main.cpp example.cpp log.cpp log.h example.h)
+
+# enable warnings
+if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+	set_target_properties(example PROPERTIES COMPILE_FLAGS "-Weverything")
+elseif (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+	set_target_properties(example PROPERTIES COMPILE_FLAGS "-Wall -Wextra")
+endif()
+
+cotire(example)
+
+# cotire sets the following properties
+get_target_property(_unitySource example COTIRE_CXX_UNITY_SOURCE)
+get_target_property(_prefixHeader example COTIRE_CXX_PREFIX_HEADER)
+get_target_property(_precompiledHeader example COTIRE_CXX_PRECOMPILED_HEADER)
+get_target_property(_unityTargetName example COTIRE_UNITY_TARGET_NAME)
+
+if (_unitySource)
+	message(STATUS "example unity source: ${_unitySource}")
+endif()
+if (_prefixHeader)
+	message(STATUS "example prefix header: ${_prefixHeader}")
+endif()
+if (_precompiledHeader)
+	message(STATUS "example precompiled header: ${_precompiledHeader}")
+endif()
+if (TARGET ${_unityTargetName})
+	message(STATUS "example unity target: ${_unityTargetName}")
+endif()

build/cmake/modules/cotire_test/src/example.cpp

@@ -0,0 +1,24 @@
+// cotire example project
+
+#include "example.h"
+
+#ifndef NDEBUG
+#include <algorithm>
+#include <iterator>
+#endif
+
+namespace example {
+
+std::string get_message() {
+	char msg_chrs[] = { 'C', 'o', 't', 'i', 'r', 'e', 'd', '!' };
+#ifdef NDEBUG
+	return std::string(&msg_chrs[0], &msg_chrs[sizeof(msg_chrs)]);
+#else
+	std::string msg;
+	msg.reserve(sizeof(msg_chrs));
+	std::copy(msg_chrs, msg_chrs + sizeof(msg_chrs), std::back_inserter(msg));
+	return msg;
+#endif
+}
+
+}

build/cmake/modules/cotire_test/src/example.h

@@ -0,0 +1,10 @@
+// cotire example project
+
+#include <string>
+
+namespace example {
+
+std::string get_message();
+
+}
+

build/cmake/modules/cotire_test/src/log.cpp

@@ -0,0 +1,17 @@
+// cotire example project
+
+#include "log.h"
+
+#include <iostream>
+
+namespace logging {
+
+void error(const std::string& msg) {
+	std::cerr << msg << std::endl;
+}
+
+void info(const std::string& msg) {
+	std::cout << msg << std::endl;
+}
+
+}

build/cmake/modules/cotire_test/src/log.h

@@ -0,0 +1,10 @@
+// cotire example project
+
+#include <string>
+
+namespace logging {
+
+void error(const std::string& msg);
+void info(const std::string& msg);
+
+}

build/cmake/modules/cotire_test/src/main.cpp

@@ -0,0 +1,12 @@
+// cotire example project main
+
+#include <string>
+
+#include "example.h"
+#include "log.h"
+
+int main()
+{
+	std::string msg = example::get_message();
+	logging::info(msg);
+}