cmake: add detection of threadsafe feature

Avoids failing test 1014 by replicating configure checks
for HAVE_ATOMIC and _WIN32_WINNT with custom CMake tests.

Reviewed-by: Marcel Raad

Follow up to #8680
Closes #9312

CMake/CurlTests.c

@@ -516,3 +516,50 @@ main() {
   return 0;
 }
 #endif
+#ifdef HAVE_ATOMIC
+/* includes start */
+#ifdef HAVE_SYS_TYPES_H
+#  include <sys/types.h>
+#endif
+#ifdef HAVE_UNISTD_H
+#  include <unistd.h>
+#endif
+#ifdef HAVE_STDATOMIC_H
+#  include <stdatomic.h>
+#endif
+/* includes end */
+
+int
+main() {
+  _Atomic int i = 1;
+  i = 0;  // Force an atomic-write operation.
+  return i;
+}
+#endif
+#ifdef HAVE_WIN32_WINNT
+/* includes start */
+#ifdef WIN32
+/*
+ * Don't include unneeded stuff in Windows headers to avoid compiler
+ * warnings and macro clashes.
+ * Make sure to define this macro before including any Windows headers.
+ */
+#  ifndef WIN32_LEAN_AND_MEAN
+#    define WIN32_LEAN_AND_MEAN
+#  endif
+#  ifndef NOGDI
+#    define NOGDI
+#  endif
+#  include "../lib/setup-win32.h"
+#endif
+/* includes end */
+
+#define enquote(x) #x
+#define expand(x) enquote(x)
+#pragma message("_WIN32_WINNT=" expand(_WIN32_WINNT))
+
+int
+main() {
+  return 0;
+}
+#endif

CMakeLists.txt

@@ -982,6 +982,7 @@ check_include_file_concat("pwd.h"            HAVE_PWD_H)
 check_include_file_concat("setjmp.h"         HAVE_SETJMP_H)
 check_include_file_concat("signal.h"         HAVE_SIGNAL_H)
 check_include_file_concat("ssl.h"            HAVE_SSL_H)
+check_include_file_concat("stdatomic.h"      HAVE_STDATOMIC_H)
 check_include_file_concat("stdbool.h"        HAVE_STDBOOL_H)
 check_include_file_concat("stdint.h"         HAVE_STDINT_H)
 check_include_file_concat("stdlib.h"         HAVE_STDLIB_H)
@@ -1143,6 +1144,7 @@ foreach(CURL_TEST
     HAVE_FILE_OFFSET_BITS
     HAVE_VARIADIC_MACROS_C99
     HAVE_VARIADIC_MACROS_GCC
+    HAVE_ATOMIC
     )
   curl_internal_test(${CURL_TEST})
 endforeach()
@@ -1159,6 +1161,19 @@ set(CMAKE_EXTRA_INCLUDE_FILES "curl/system.h")
 check_type_size("curl_off_t"  SIZEOF_CURL_OFF_T)
 set(CMAKE_EXTRA_INCLUDE_FILES "")
 
+if(WIN32)
+  # detect actual value of _WIN32_WINNT and store as HAVE_WIN32_WINNT
+  curl_internal_test(HAVE_WIN32_WINNT)
+  if(HAVE_WIN32_WINNT)
+    string(REGEX MATCH ".*_WIN32_WINNT=0x[0-9a-fA-F]+" OUTPUT "${OUTPUT}")
+    string(REGEX REPLACE ".*_WIN32_WINNT=" "" OUTPUT "${OUTPUT}")
+    math(EXPR HAVE_WIN32_WINNT "${OUTPUT}" OUTPUT_FORMAT DECIMAL)
+    message(STATUS "Found _WIN32_WINNT=${OUTPUT} (${HAVE_WIN32_WINNT})")
+  endif()
+  # avoid storing HAVE_WIN32_WINNT in CMake cache
+  unset(HAVE_WIN32_WINNT CACHE)
+endif()
+
 set(CMAKE_REQUIRED_FLAGS)
 
 foreach(CURL_TEST
@@ -1417,6 +1432,8 @@ _add_if("HTTP3"         USE_NGTCP2 OR USE_QUICHE)
 _add_if("MultiSSL"      CURL_WITH_MULTI_SSL)
 _add_if("HTTPS-proxy"   SSL_ENABLED AND (USE_OPENSSL OR USE_GNUTLS OR USE_NSS))
 _add_if("unicode"       ENABLE_UNICODE)
+_add_if("threadsafe"    HAVE_ATOMIC OR (WIN32 AND
+                        HAVE_WIN32_WINNT GREATER_EQUAL 0x600))
 string(REPLACE ";" " " SUPPORT_FEATURES "${_items}")
 message(STATUS "Enabled features: ${SUPPORT_FEATURES}")
 

lib/curl_config.h.cmake

@@ -156,6 +156,9 @@
 /* Define to 1 if you have the <assert.h> header file. */
 #cmakedefine HAVE_ASSERT_H 1
 
+/* Define to 1 if you have _Atomic support. */
+#cmakedefine HAVE_ATOMIC 1
+
 /* Define to 1 if you have the `fchmod' function. */
 #cmakedefine HAVE_FCHMOD 1
 
@@ -472,6 +475,9 @@
 /* Define to 1 if you have the <ssl.h> header file. */
 #cmakedefine HAVE_SSL_H 1
 
+/* Define to 1 if you have the <stdatomic.h> header file. */
+#cmakedefine HAVE_STDATOMIC_H 1
+
 /* Define to 1 if you have the <stdbool.h> header file. */
 #cmakedefine HAVE_STDBOOL_H 1