Makefile: Fix command line limits for static libs

I have been hitting the Windows command-line limit when cross-compiling
static library (POCO) and having more than 8000 characters in the call
to "ar". Calculating exact limits here are tricky, since this particular
limit will only take into account object file strings, which is correct
for response files, but not for the archive rules (link.txt files),
since they also contain the call to "ar" and its arguments.
Also, there can be other additional arguments if "ar" tool is wrapped
into something else, so it is a good idea to leave more space than
trying to exactly fit the limit.
Since response files use half of the limit as a heuristic, we reproduce
it here for consistency.

1 files changed, 9 insertions, 4 deletions

diff --git a/Source/cmMakefileLibraryTargetGenerator.cxx b/Source/cmMakefileLibraryTargetGenerator.cxx
index 27fae04..c538992 100644
--- a/Source/cmMakefileLibraryTargetGenerator.cxx
+++ b/Source/cmMakefileLibraryTargetGenerator.cxx
@@ -5,6 +5,7 @@
 #include <algorithm>
 #include <memory> // IWYU pragma: keep
 #include <sstream>
+#include <stddef.h>
 #include <vector>
 
 #include "cmGeneratedFileStream.h"
@@ -732,10 +733,14 @@ void cmMakefileLibraryTargetGenerator::WriteLibraryRules(
     // Archiving rules never use a response file.
     useResponseFileForObjects = false;
 
-    // Limit the length of individual object lists to less than the
-    // 32K command line length limit on Windows.  We could make this a
-    // platform file variable but this should work everywhere.
-    archiveCommandLimit = 30000;
+    // Limit the length of individual object lists to less than half of
+    // the command line length limit (leaving half for other flags).
+    // This may result in several calls to the archiver.
+    if (size_t limit = cmSystemTools::CalculateCommandLineLengthLimit()) {
+      archiveCommandLimit = limit / 2;
+    } else {
+      archiveCommandLimit = 8000;
+    }
   }
 
   // Expand the rule variables.