Ninja,Makefile: Unify command line limit logic

Move the logic to cmSystemTools to be shared among the generators.
Revise the implementation and add comments justifying each possible
source for a limit.

Source/cmNinjaNormalTargetGenerator.cxx

@@ -5,11 +5,9 @@
 #include <algorithm>
 #include <assert.h>
 #include <iterator>
-#include <limits>
 #include <map>
 #include <set>
 #include <sstream>
-#include <stddef.h>
 
 #include "cmAlgorithms.h"
 #include "cmCustomCommand.h"
@@ -35,10 +33,6 @@
 #include "cm_auto_ptr.hxx"
 #include "cmake.h"
 
-#ifndef _WIN32
-#include <unistd.h>
-#endif
-
 cmNinjaNormalTargetGenerator::cmNinjaNormalTargetGenerator(
   cmGeneratorTarget* target)
   : cmNinjaTargetGenerator(target)
@@ -546,36 +540,6 @@ std::vector<std::string> cmNinjaNormalTargetGenerator::ComputeLinkCmd()
   return std::vector<std::string>();
 }
 
-static int calculateCommandLineLengthLimit(int linkRuleLength)
-{
-  static int const limits[] = {
-#ifdef _WIN32
-    8000,
-#endif
-#if defined(__linux)
-    // #define MAX_ARG_STRLEN (PAGE_SIZE * 32) in Linux's binfmts.h
-    ((int)sysconf(_SC_PAGESIZE) * 32) - 1000,
-#endif
-    std::numeric_limits<int>::max()
-  };
-
-  size_t const arrSz = cmArraySize(limits);
-  int sz = *std::min_element(limits, limits + arrSz);
-#if defined(_SC_ARG_MAX)
-  // for instance ARG_MAX is 2096152 on Ubuntu or 262144 on Mac
-  int const szArgMax = static_cast<int>(sysconf(_SC_ARG_MAX));
-  // a return value of -1 signifies an unrestricted value
-  if (szArgMax != -1) {
-    sz = std::min(sz, szArgMax - 1000);
-  }
-#endif
-  if (sz == std::numeric_limits<int>::max()) {
-    return 0;
-  }
-
-  return sz - linkRuleLength;
-}
-
 void cmNinjaNormalTargetGenerator::WriteDeviceLinkStatement()
 {
   cmGeneratorTarget& genTarget = *this->GetGeneratorTarget();
@@ -761,8 +725,9 @@ void cmNinjaNormalTargetGenerator::WriteDeviceLinkStatement()
 
   // Device linking currently doesn't support response files so
   // do not check if the user has explicitly forced a response file.
-  int const commandLineLengthLimit = calculateCommandLineLengthLimit(
-    globalGen.GetRuleCmdLength(this->LanguageLinkerDeviceRule()));
+  int const commandLineLengthLimit =
+    static_cast<int>(cmSystemTools::CalculateCommandLineLengthLimit()) -
+    globalGen.GetRuleCmdLength(this->LanguageLinkerDeviceRule());
 
   const std::string rspfile =
     std::string(cmake::GetCMakeFilesDirectoryPostSlash()) +
@@ -1048,8 +1013,9 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
     !(this->TargetLinkLanguage == "RC" || this->TargetLinkLanguage == "CUDA");
   int commandLineLengthLimit = -1;
   if (!lang_supports_response || !this->ForceResponseFile()) {
-    commandLineLengthLimit = calculateCommandLineLengthLimit(
-      globalGen.GetRuleCmdLength(this->LanguageLinkerRule()));
+    commandLineLengthLimit =
+      static_cast<int>(cmSystemTools::CalculateCommandLineLengthLimit()) -
+      globalGen.GetRuleCmdLength(this->LanguageLinkerRule());
   }
 
   const std::string rspfile =