This patch provides an update so that nhc98 can be built and works with
a modern C compiler (GCC 11) and libc (glibc 2.33).

diff --git a/Makefile.inc b/Makefile.inc
index 4fbd47a..5bce5c9 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -1,6 +1,10 @@
 ### Configurable variables:
 
-OPT = -O3
+# We want C89 semantics plus C++-style comments and things like the
+# 'setjmp_buf' and 'u_short' types.  More importantly, build with '-O1'
+# only to avoid modern optimizations that break the code.
+OPT = -O1 -std=gnu89 -D_GNU_SOURCE=1
+
 #ARCH = -m32
 ARCH = 
 
diff --git a/script/nhc98heap.c b/script/nhc98heap.c
index 534010e..a30d5cd 100644
--- a/script/nhc98heap.c
+++ b/script/nhc98heap.c
@@ -1,5 +1,6 @@
 #include <stdlib.h>
 #include <stdio.h>
+#include <ctype.h>
 main(int argc, char **argv)
 {
   int prefix = 1;
diff --git a/src/runtime/Kernel/collector.c b/src/runtime/Kernel/collector.c
index b95a273..1f879c5 100644
--- a/src/runtime/Kernel/collector.c
+++ b/src/runtime/Kernel/collector.c
@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 #include "node.h"
 /*#include "newmacros.h"  -- already included in node.h */
 /*#include "runtime.h"    -- already included in node.h */
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