msvc: tidy up _CRT_*_NO_DEPRECATE definitions

Dedupe and migrate MSVC-specific warning suppressions to `curl_setup.h`.
Make cmake set `_CRT_SECURE_NO_DEPRECATE` for examples and standalone
tests, and stop setting `_CRT_NONSTDC_NO_DEPRECATE` for them.

Details:
- drop version guards. On ancient MSVC version these macro are a no-op.
- move to `curl_setup.h` from `config-win32*.h`.
- sync macro values with CMake.
- cmake: stop setting them globally in favour of `curl_setup.h`.
- cmake: re-add these macros to `docs/examples` and `tests/http/clients`,
  which do not use `curl_setup.h`.
- cmake: drop `_CRT_NONSTDC_NO_DEPRECATE` for examples and tests.
  They build fine without.
- update comments.

Closes #15960

CMakeLists.txt

@@ -1892,7 +1892,6 @@ if(MSVC)
   # Disable default manifest added by CMake
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /MANIFEST:NO")
 
-  add_definitions("-D_CRT_SECURE_NO_DEPRECATE" "-D_CRT_NONSTDC_NO_DEPRECATE")
   if(CMAKE_C_FLAGS MATCHES "/W[0-4]")
     string(REGEX REPLACE "/W[0-4]" "/W4" CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
   else()

docs/examples/CMakeLists.txt

@@ -33,7 +33,7 @@ foreach(_target IN LISTS check_PROGRAMS)
   add_executable(${_target_name} EXCLUDE_FROM_ALL "${_target}.c")
   add_dependencies(curl-examples ${_target_name})
   target_link_libraries(${_target_name} ${LIB_SELECTED} ${CURL_LIBS})
-  target_compile_definitions(${_target_name} PRIVATE "CURL_NO_OLDIES")
+  target_compile_definitions(${_target_name} PRIVATE "CURL_NO_OLDIES" "$<$<BOOL:MSVC>:_CRT_SECURE_NO_DEPRECATE>")
   if(LIB_SELECTED STREQUAL LIB_STATIC AND WIN32)
     set_property(TARGET ${_target_name} APPEND PROPERTY COMPILE_DEFINITIONS "CURL_STATICLIB")
   endif()

lib/config-win32.h

@@ -293,12 +293,6 @@
 #define HAVE_LONGLONG 1
 #endif
 
-/* Define to avoid VS2005 complaining about portable C functions. */
-#if defined(_MSC_VER) && (_MSC_VER >= 1400)
-#define _CRT_SECURE_NO_DEPRECATE 1
-#define _CRT_NONSTDC_NO_DEPRECATE 1
-#endif
-
 /* mingw-w64 and visual studio >= 2005 (MSVCR80)
    all default to 64-bit time_t unless _USE_32BIT_TIME_T is defined */
 #if (defined(_MSC_VER) && (_MSC_VER >= 1400)) || defined(__MINGW32__)

lib/config-win32ce.h

@@ -218,12 +218,6 @@
 /* Undef keyword 'const' if it does not work. */
 /* #undef const */
 
-/* Define to avoid VS2005 complaining about portable C functions. */
-#if defined(_MSC_VER) && (_MSC_VER >= 1400)
-#define _CRT_SECURE_NO_DEPRECATE 1
-#define _CRT_NONSTDC_NO_DEPRECATE 1
-#endif
-
 /* VS2005 and later default size for time_t is 64-bit, unless */
 /* _USE_32BIT_TIME_T has been defined to get a 32-bit time_t. */
 #if defined(_MSC_VER) && (_MSC_VER >= 1400)

lib/curl_setup.h

@@ -85,13 +85,17 @@
 #endif
 #endif
 
-/*
- * Disable Visual Studio warnings:
- * 4127 "conditional expression is constant"
- */
 #ifdef _MSC_VER
+/* Disable Visual Studio warnings: 4127 "conditional expression is constant" */
 #pragma warning(disable:4127)
+/* Avoid VS2005 and upper complaining about portable C functions. */
+#ifndef _CRT_NONSTDC_NO_DEPRECATE
+#define _CRT_NONSTDC_NO_DEPRECATE  /* for strdup(), write(), etc. */
 #endif
+#ifndef _CRT_SECURE_NO_DEPRECATE
+#define _CRT_SECURE_NO_DEPRECATE  /* for fopen(), getenv(), etc. */
+#endif
+#endif /* _MSC_VER */
 
 #ifdef _WIN32
 /*

tests/http/clients/CMakeLists.txt

@@ -38,7 +38,7 @@ foreach(_target IN LISTS check_PROGRAMS)
     "${PROJECT_SOURCE_DIR}/lib"  # for "curl_setup.h"
   )
   target_link_libraries(${_target_name} ${LIB_SELECTED} ${CURL_LIBS})
-  target_compile_definitions(${_target_name} PRIVATE "CURL_NO_OLDIES")
+  target_compile_definitions(${_target_name} PRIVATE "CURL_NO_OLDIES" "$<$<BOOL:MSVC>:_CRT_SECURE_NO_DEPRECATE>")
   if(LIB_SELECTED STREQUAL LIB_STATIC AND WIN32)
     set_property(TARGET ${_target_name} APPEND PROPERTY COMPILE_DEFINITIONS "CURL_STATICLIB")
   endif()