CMake: Add builtins

CMakeLists.txt

@@ -42,6 +42,7 @@ if (NOT WIN32)
     find_package(Fontconfig)
     find_package(ICU OPTIONAL_COMPONENTS i18n lx)
     find_package(XDG_basedir)
+    find_package(Builtins)
 endif (NOT WIN32)
 if (APPLE)
     find_package(Iconv)

cmake/FindBuiltins.cmake

@@ -0,0 +1,34 @@
+include(CheckCXXSourceCompiles)
+
+check_cxx_source_compiles("
+    int main() {
+        return __builtin_popcountll(__builtin_popcountl(__builtin_popcount(__builtin_ctz(1))));
+    }"
+    BITMATH_BUILTINS_FOUND
+)
+
+if (BITMATH_BUILTINS_FOUND)
+    add_compile_options(
+        -DWITH_BITMATH_BUILTINS
+    )
+endif (BITMATH_BUILTINS_FOUND)
+
+check_cxx_source_compiles("
+#include <cstdint>
+int main() {
+    int64_t a = 0;
+    int64_t b = 0;
+    int64_t c = 0;
+    bool res1 = __builtin_add_overflow(a, b, &c);
+    bool res2 = __builtin_sub_overflow(a, b, &c);
+    bool res3 = __builtin_mul_overflow(a, b, &c);
+    return (res1 || res2 || res3) ? 1 : 0;
+}"
+    OVERFLOW_BUILTINS_FOUND
+)
+
+if (OVERFLOW_BUILTINS_FOUND)
+    add_compile_options(
+        -DWITH_OVERFLOW_BUILTINS
+    )
+endif (OVERFLOW_BUILTINS_FOUND)