cmake: allow building tests in unity mode

Makes building tests noticeably faster.

Apply changes/fixes/workarounds to make Unity work:
- rename test variables to avoid collisions or shadowing each other when
  combined into single units.
- add workaround to avoid applying `lib/memdebug.h` overrides to system
  headers declaring/defining `getaddrinfo()`/`freeaddrinfo()` for
  `tests/server/resolve.c`. This replaces a previous workaround that
  worked for that specific source.
- rename test macro `CTRL` clashing with Cygwin `sys/ioctl.h`.
- add include guard to `test.h`.

Also:
- exclude `tests/http/clients` which are all single-source. (like
  `docs/examples`.)

Build time improvements for tests:
- AppVeyor CI:
  - MSVC 2008, 2010: 1 minute faster (4m8s -> 2m56s, 3m19s -> 2m24s)
  - MSVC 2022 arm64: 3.5 minutes faster (10m18s -> 6m48s)
  before: https://ci.appveyor.com/project/curlorg/curl/builds/50522785
  after: https://ci.appveyor.com/project/curlorg/curl/builds/50522942
- GHA:
  - Cygwin: 1.5 minutes faster (3m13s -> 1m43s)
    before: https://github.com/curl/curl/actions/runs/10681535327/job/29605384398
    after: https://github.com/curl/curl/actions/runs/10680818726/job/29603130637
  - Windows:
    before: https://github.com/curl/curl/actions/runs/10680818713
    after: https://github.com/curl/curl/actions/runs/10683850187
    - MSYS2, mingw-w64: 1 minute faster
    - MSVC: 30 seconds faster (3m17s -> 2m48s)
  - macOS: double speed (39s -> 18s)
    before: https://github.com/curl/curl/actions/runs/10680818753/job/29603133447
    after: https://github.com/curl/curl/actions/runs/10683850174/job/29612914515
  - Linux: almost double speed (30/31s -> 18s)
    before: https://github.com/curl/curl/actions/runs/10681535311/job/29605387156
    after: https://github.com/curl/curl/actions/runs/10680818721/job/29603133976
  - non-native: no obvious effect.
    before: https://github.com/curl/curl/actions/runs/10680818722
    after: https://github.com/curl/curl/actions/runs/10683850187
  - Old Linux: Unity mode not supported by old CMake, no effect.

Closes #14765

tests/libtest/CMakeLists.txt

@@ -26,6 +26,8 @@
 transform_makefile_inc("Makefile.inc" "${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 include("${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 
+set_source_files_properties("../../lib/curl_multibyte.c" PROPERTIES SKIP_UNITY_BUILD_INCLUSION ON)
+
 foreach(_target IN LISTS noinst_PROGRAMS)
   if(DEFINED ${_target}_SOURCES)
     set(_sources ${${_target}_SOURCES})

tests/libtest/first.c

@@ -120,7 +120,7 @@ static void memory_tracking_init(void)
 #endif
 
 /* returns a hexdump in a static memory area */
-char *hexdump(const unsigned char *buffer, size_t len)
+char *hexdump(const unsigned char *buf, size_t len)
 {
   static char dump[200 * 3 + 1];
   char *p = dump;
@@ -128,7 +128,7 @@ char *hexdump(const unsigned char *buffer, size_t len)
   if(len > 200)
     return NULL;
   for(i = 0; i < len; i++, p += 3)
-    msnprintf(p, 4, "%02x ", buffer[i]);
+    msnprintf(p, 4, "%02x ", buf[i]);
   return dump;
 }
 

tests/libtest/lib553.c

@@ -55,7 +55,7 @@ static size_t myreadfunc(char *ptr, size_t size, size_t nmemb, void *stream)
 #define NUM_HEADERS 8
 #define SIZE_HEADERS 5000
 
-static char buf[SIZE_HEADERS + 100];
+static char testbuf[SIZE_HEADERS + 100];
 
 CURLcode test(char *URL)
 {
@@ -77,10 +77,10 @@ CURLcode test(char *URL)
   }
 
   for(i = 0; i < NUM_HEADERS; i++) {
-    int len = msnprintf(buf, sizeof(buf), "Header%d: ", i);
-    memset(&buf[len], 'A', SIZE_HEADERS);
-    buf[len + SIZE_HEADERS] = 0; /* null-terminate */
-    hl = curl_slist_append(headerlist,  buf);
+    int len = msnprintf(testbuf, sizeof(testbuf), "Header%d: ", i);
+    memset(&testbuf[len], 'A', SIZE_HEADERS);
+    testbuf[len + SIZE_HEADERS] = 0; /* null-terminate */
+    hl = curl_slist_append(headerlist, testbuf);
     if(!hl)
       goto test_cleanup;
     headerlist = hl;

tests/libtest/lib677.c

@@ -28,7 +28,7 @@
 #include "memdebug.h"
 
 static const char cmd[] = "A1 IDLE\r\n";
-static char buf[1024];
+static char testbuf[1024];
 
 CURLcode test(char *URL)
 {
@@ -101,9 +101,9 @@ CURLcode test(char *URL)
           pos = 0;
         }
       }
-      else if(pos < (ssize_t)sizeof(buf)) {
+      else if(pos < (ssize_t)sizeof(testbuf)) {
         CURLcode ec;
-        ec = curl_easy_recv(curl, buf + pos, sizeof(buf) - pos, &len);
+        ec = curl_easy_recv(curl, testbuf + pos, sizeof(testbuf) - pos, &len);
         if(ec == CURLE_AGAIN) {
           continue;
         }
@@ -122,7 +122,7 @@ CURLcode test(char *URL)
   }
 
   if(state) {
-    fwrite(buf, pos, 1, stdout);
+    fwrite(testbuf, pos, 1, stdout);
     putchar('\n');
   }
 

tests/libtest/test.h

@@ -1,3 +1,5 @@
+#ifndef HEADER_CURL_TEST_H
+#define HEADER_CURL_TEST_H
 /***************************************************************************
  *                                  _   _ ____  _
  *  Project                     ___| | | |  _ \| |
@@ -498,3 +500,5 @@ extern int unitfail;
   }
 
 /* ---------------------------------------------------------------- */
+
+#endif /* HEADER_CURL_TEST_H */