Fix bug in error handling where __sub would be clobbered.
diff --git a/share/jmk/jmk.m4 b/share/jmk/jmk.m4
index be6fe3d..aa3ad79 100644
--- a/share/jmk/jmk.m4
+++ b/share/jmk/jmk.m4
@@ -45,7 +45,7 @@
$1, `debug', `CFLAGS += -g
ASMFLAGS += -Fdwarf',
$1, `32', `CFLAGS += -m32',
- $1, `warn', `CFLAGS += -Wall -Wno-unused-function -Wno-unused-variable -Wno-incompatible-pointer-types',
+ $1, `warn', `CFLAGS += -Wall -Wextra -Wno-unused-function -Wno-unused-variable -Wno-incompatible-pointer-types',
$1, `nasm', `ASM = nasm',
$1, `glossaries', `LATEX_MAKE_GLOSSARIES = 1',
$1, xelatex, `LATEXC = xelatex')')