cmake: honor custom CMAKE_UNITY_BUILD_BATCH_SIZE

[vszakats]

This value tells how many sources files to bundle in a single "unity"
compilation unit.

The CMake default is 8 sources, curl's CMake set this to 0, meaning
to bundle all sources into a single unit.

This patch makes it possible to override the 0 value, and potentially
optimize the build process further by better utilizing multiple cores
in conjunction with make -jN.

The number of sources in lib is 172 at the time of writing this. For
a 12-core CPU, this can give a job for them all:
-DCMAKE_UNITY_BUILD_BATCH_SIZE=15

(Compile time may be affected by a bunch of other factors.)

[bagder]

For some reason this feature breaks the build for me in ways it does not for "normal" unity build:

$ cmake -B build -DCMAKE_UNITY_BUILD=ON -DCMAKE_UNITY_BUILD_BATCH_SIZE=15
$ cd build
$ make -sj
...

/home/dast/src/curl/src/tool_getparam.c: In function ‘getparameter’:
/home/dast/src/curl/src/tool_getparam.c:2409:11: error: implicit declaration of function ‘msnprintf’; did you mean ‘vsnprintf’? [-Wimplicit-function-declaration]
 2409 |           msnprintf(buffer, sizeof(buffer), "%" CURL_FORMAT_CURL_OFF_T "-",
      |           ^~~~~~~~~
      |           vsnprintf
/home/dast/src/curl/src/tool_getparam.c:2409:11: warning: nested extern declaration of ‘msnprintf’ [-Wnested-externs]
In file included from /home/dast/src/curl/build/src/CMakeFiles/curl.dir/Unity/unity_1_c.c:28:
/home/dast/src/curl/src/tool_ipfs.c: In function ‘ipfs_gateway’:
/home/dast/src/curl/src/tool_ipfs.c:83:19: error: implicit declaration of function ‘aprintf’; did you mean ‘dprintf’? [-Wimplicit-function-declaration]
   83 |       ipfs_path = aprintf("%s/.ipfs/", home);
      |                   ^~~~~~~
      |                   dprintf
/home/dast/src/curl/src/tool_ipfs.c:83:19: warning: nested extern declaration of ‘aprintf’ [-Wnested-externs]
/home/dast/src/curl/src/tool_ipfs.c:83:17: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
   83 |       ipfs_path = aprintf("%s/.ipfs/", home);
      |                 ^
/home/dast/src/curl/src/tool_ipfs.c:90:30: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
   90 |   gateway_composed_file_path = aprintf("%sgateway", ipfs_path);
      |                              ^
/home/dast/src/curl/src/tool_ipfs.c: In function ‘ipfs_url_rewrite’:
/home/dast/src/curl/src/tool_ipfs.c:240:14: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  240 |   pathbuffer = aprintf("%s%s/%s%s", gwpath, protocol, cid,
      |              ^
In file included from /home/dast/src/curl/build/src/CMakeFiles/curl.dir/Unity/unity_1_c.c:43:
/home/dast/src/curl/src/tool_operate.c: In function ‘single_transfer’:
/home/dast/src/curl/src/tool_operate.c:986:20: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  986 |             header = aprintf("If-None-Match: %s", etag_from_file);
      |                    ^
/home/dast/src/curl/src/tool_operate.c:990:20: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  990 |             header = aprintf("If-None-Match: \"\"");
      |                    ^
/home/dast/src/curl/src/tool_operate.c:1197:23: error: initialization of ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
 1197 |             char *d = aprintf("%s/%s", config->output_dir, per->outfile);
      |                       ^~~~~~~
In file included from /home/dast/src/curl/build/src/CMakeFiles/curl.dir/Unity/unity_1_c.c:46:
/home/dast/src/curl/src/tool_operhlp.c: In function ‘add_file_name_to_url’:
/home/dast/src/curl/src/tool_operhlp.c:144:19: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  144 |           newpath = aprintf("%s%s", path, encfile);
      |                   ^
/home/dast/src/curl/src/tool_operhlp.c:147:19: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  147 |           newpath = aprintf("%s/%s", path, encfile);
      |                   ^
make[2]: *** [src/CMakeFiles/curl.dir/build.make:115: src/CMakeFiles/curl.dir/Unity/unity_1_c.c.o] Error 1

[vszakats]

Right, this shouldn't of course happen, but with this setting there is any number of new mash-up combinations, and it isn't without side-effects. I could replicate, and having a look.

[bagder]

I don't think you need to spend a lot of energy on fixing that if it turns out cumbersome. It's such a niche thing.

[vszakats]

I think it's useful because issues like this may pop up in other places in the future. Even in UNITY_BATCH=0.

In this case it was the common one where a header guarded against multiple inclusions has two operating modes depending on a macro set before including it: curlx.h and ENABLE_CURLX_PRINTF.

With BATCH=15 a source included it first without setting ENABLE_CURLX_PRINTF, so the next source trying to get these redefines did not get them!

Basically the same as the libssh.h issue fixed yesterday.

This should fix it, though the full fix will be a little longer, by removing the per-file #define ENABLE_CURLX_PRINTF lines:

--- a/src/tool_setup.h
+++ b/src/tool_setup.h
@@ -25,6 +25,7 @@
  ***************************************************************************/
 
 #define CURL_NO_OLDIES
+#define ENABLE_CURLX_PRINTF
 
 /*
  * curl_setup.h may define preprocessor macros such as _FILE_OFFSET_BITS and