Don't set SyAllocPool = 0 for Cygwin, but do use MAP_NORESERVE for mmaps

on Cygwin

Using MAP_NORESERVE on Cygwin prevents the need to commit physical pages
for the entirety of mmap'd regions until they are actually used.

src/sysmem.c

@@ -280,6 +280,12 @@ int SyTryToIncreasePool(void)
 #define MAP_ANONYMOUS MAP_ANON
 #endif
 
+#ifdef SYS_IS_CYGWIN32
+#define GAP_MMAP_FLAGS MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE
+#else
+#define GAP_MMAP_FLAGS MAP_PRIVATE|MAP_ANONYMOUS
+#endif
+
 static void *SyMMapStart = NULL; /* Start of mmap'ed region for POOL */
 static void *SyMMapEnd; /* End of mmap'ed region for POOL */
 static void *SyMMapAdvised; /* We have already advised about non-usage
@@ -341,15 +347,15 @@ static void * SyAnonMMap(size_t size)
  size = SyRoundUpToPagesize(size);
 #ifdef SYS_IS_64_BIT
  /* The following is at 16 Terabyte: */
- result = mmap((void *) (16L*1024*1024*1024*1024), size, 
- PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+ result = mmap((void *) (16L*1024*1024*1024*1024), size,
+ PROT_READ|PROT_WRITE, GAP_MMAP_FLAGS, -1, 0);
  if (result == MAP_FAILED) {
  result = mmap(NULL, size, PROT_READ|PROT_WRITE,
- MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+ GAP_MMAP_FLAGS, -1, 0);
  }
 #else
  result = mmap(NULL, size, PROT_READ|PROT_WRITE,
- MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+ GAP_MMAP_FLAGS, -1, 0);
 #endif
  if (result == MAP_FAILED)
  result = NULL;
@@ -370,7 +376,7 @@ static int SyTryToIncreasePool(void)
  size = (Int) SyMMapEnd - (Int) SyMMapStart;
  newchunk = SyRoundUpToPagesize(size/2);
  result = mmap(SyMMapEnd, newchunk, PROT_READ|PROT_WRITE,
- MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+ GAP_MMAP_FLAGS, -1, 0);
  if (result == MAP_FAILED) return -1;
  if (result != SyMMapEnd) {
  munmap(result,newchunk);

src/system.c

@@ -1072,11 +1072,7 @@ void InitSystem (
 #else
  SyStorMin = 64 * 1024L;
  SyStorMax = 1024*1024L; /* This is in kB! */
-#ifdef SYS_IS_CYGWIN32
- SyAllocPool = 0; /* works better on cygwin */
-#else
  SyAllocPool = 1536L*1024*1024; /* Note this is in bytes! */
-#endif
 #endif
  SyStorOverrun = 0;
  SyStorKill = 0;