I am uploading a NMU with the attached changes to fix this.
diff -Nru gmemusage-0.2/Makefile gmemusage-0.2/Makefile
--- gmemusage-0.2/Makefile 2024-06-09 16:42:55.000000000 +0000
+++ gmemusage-0.2/Makefile 1998-01-14 16:45:13.000000000 +0000
@@ -26,7 +26,7 @@
# You shouldn't need to modify anything below this line
#
OPTIONS = $(BELL_ON_UNKNOWN_KEYPRESS) $(USE_PASTELS) $(SAVE_XSERVER_MEMORY)
-CFLAGS = $(OPTIM) -Wall $(OPTIONS) -g
+CFLAGS = $(OPTIM) -Wall $(OPTIONS)
LDFLAGS = $(OPTIM)
LIBX11 = $(LIBX11DIR) -lX11
LIBS = $(LIBX11)
diff -Nru gmemusage-0.2/debian/changelog gmemusage-0.2/debian/changelog
--- gmemusage-0.2/debian/changelog 2024-06-09 16:42:55.000000000 +0000
+++ gmemusage-0.2/debian/changelog 2024-06-09 16:24:40.000000000 +0000
@@ -1,3 +1,11 @@
+gmemusage (0.2-11.1) unstable; urgency=medium
+
+ * Non-maintainer upload
+ * Convert to source format 3.0 (closes: #1007369)
+ * Add missing includes (closes: #1066560)
+
+ -- Bastian Germann <b...@debian.org> Sun, 09 Jun 2024 16:24:40 +0000
+
gmemusage (0.2-11) unstable; urgency=low
* Adopt the package (Closes: #486759).
diff -Nru gmemusage-0.2/debian/patches/10_misc.patch
gmemusage-0.2/debian/patches/10_misc.patch
--- gmemusage-0.2/debian/patches/10_misc.patch 2024-06-09 16:42:55.000000000
+0000
+++ gmemusage-0.2/debian/patches/10_misc.patch 2024-06-09 16:24:40.000000000
+0000
@@ -64,6 +64,14 @@
#if 0
--- gmemusage-0.2.orig/proc.c
+++ gmemusage-0.2/proc.c
+@@ -7,6 +7,7 @@
+ * See file COPYING (included in this distribution) for copyright information.
+ */
+ #include <stdio.h>
++#include <stdlib.h>
+ #include <string.h>
+ #include <sys/types.h>
+ #include <dirent.h>
@@ -23,6 +23,9 @@
/*
* Set values for various memory usages
diff -Nru gmemusage-0.2/debian/patches/20_makefile.patch
gmemusage-0.2/debian/patches/20_makefile.patch
--- gmemusage-0.2/debian/patches/20_makefile.patch 2024-06-09
16:42:55.000000000 +0000
+++ gmemusage-0.2/debian/patches/20_makefile.patch 2024-06-09
16:24:40.000000000 +0000
@@ -1,5 +1,5 @@
---- Makefile.orig 2008-11-28 18:37:30.000000000 +0100
-+++ Makefile 2008-11-28 18:38:01.000000000 +0100
+--- memusage-0.2.orig/Makefile 2008-11-28 18:37:30.000000000 +0100
++++ memusage-0.2/Makefile 2008-11-28 18:38:01.000000000 +0100
@@ -19,15 +19,12 @@
# Change these variables as necessary
#
@@ -11,7 +11,7 @@
# You shouldn't need to modify anything below this line
#
OPTIONS = $(BELL_ON_UNKNOWN_KEYPRESS) $(USE_PASTELS) $(SAVE_XSERVER_MEMORY)
--CFLAGS = $(OPTIM) -Wall $(OPTIONS) -g
+-CFLAGS = $(OPTIM) -Wall $(OPTIONS)
-LDFLAGS = $(OPTIM)
LIBX11 = $(LIBX11DIR) -lX11
LIBS = $(LIBX11)
diff -Nru gmemusage-0.2/debian/patches/add-includes.patch
gmemusage-0.2/debian/patches/add-includes.patch
--- gmemusage-0.2/debian/patches/add-includes.patch 1970-01-01
00:00:00.000000000 +0000
+++ gmemusage-0.2/debian/patches/add-includes.patch 2024-06-09
16:24:40.000000000 +0000
@@ -0,0 +1,15 @@
+Description: Add missing includes
+Author: Bastian Germann <b...@debian.org>
+Bug-Debian: https://bugs.debian.org/1066560
+---
+--- gmemusage-0.2.orig/hash.c
++++ gmemusage-0.2/hash.c
+@@ -7,6 +7,8 @@
+ * See file COPYING (included in this distribution) for copyright information.
+ */
+ #include <stdio.h>
++#include <stdlib.h>
++#include <string.h>
+ #include <malloc.h>
+ #include "common.h"
+
diff -Nru gmemusage-0.2/debian/patches/series
gmemusage-0.2/debian/patches/series
--- gmemusage-0.2/debian/patches/series 1970-01-01 00:00:00.000000000 +0000
+++ gmemusage-0.2/debian/patches/series 2024-06-09 16:24:40.000000000 +0000
@@ -0,0 +1,3 @@
+10_misc.patch
+20_makefile.patch
+add-includes.patch
diff -Nru gmemusage-0.2/debian/rules gmemusage-0.2/debian/rules
--- gmemusage-0.2/debian/rules 2024-06-09 16:42:55.000000000 +0000
+++ gmemusage-0.2/debian/rules 2024-06-09 16:24:17.000000000 +0000
@@ -2,7 +2,6 @@
include /usr/share/cdbs/1/rules/debhelper.mk
include /usr/share/cdbs/1/class/makefile.mk
-include /usr/share/cdbs/1/rules/simple-patchsys.mk
DEB_INSTALL_MANPAGES_gmemusage := gmemusage.1
diff -Nru gmemusage-0.2/debian/source/format gmemusage-0.2/debian/source/format
--- gmemusage-0.2/debian/source/format 1970-01-01 00:00:00.000000000 +0000
+++ gmemusage-0.2/debian/source/format 2024-06-09 16:21:10.000000000 +0000
@@ -0,0 +1 @@
+3.0 (quilt)
