Index: lib/libc/stdlib/Makefile.inc
===================================================================
--- lib/libc/stdlib/Makefile.inc
+++ lib/libc/stdlib/Makefile.inc
@@ -4,7 +4,7 @@
 # machine-independent stdlib sources
 .PATH: ${LIBC_SRCTOP}/${LIBC_ARCH}/stdlib ${LIBC_SRCTOP}/stdlib
 
-MISRCS+=_Exit.c a64l.c abort.c abs.c atexit.c atof.c atoi.c atol.c atoll.c \
+MISRCS+=C99_Exit.c a64l.c abort.c abs.c atexit.c atof.c atoi.c atol.c atoll.c \
 	bsearch.c cxa_thread_atexit.c div.c exit.c getenv.c getopt.c getopt_long.c \
 	getsubopt.c hcreate.c hcreate_r.c hdestroy_r.c heapsort.c heapsort_b.c \
 	hsearch_r.c imaxabs.c imaxdiv.c \
@@ -16,6 +16,13 @@
 	strtol.c strtoll.c strtoq.c strtoul.c strtonum.c strtoull.c \
         strtoumax.c strtouq.c system.c tdelete.c tfind.c tsearch.c twalk.c
 
+# Work around an issue on case-insensitive file systems.
+# libc has both _Exit.c and _exit.s and they both yield
+# _exit.o (case insensitively speaking).
+CLEANFILES+=C99_Exit.c
+C99_Exit.c: ${LIBC_SRCTOP}/stdlib/_Exit.c .NOMETA
+	ln -sf ${.ALLSRC} ${.TARGET}
+
 SYM_MAPS+= ${LIBC_SRCTOP}/stdlib/Symbol.map
 
 # machine-dependent stdlib sources