请问出现下列警告是什么原因造成的？

要求Makefile指定正确的X libraies位置，我装的是RedHat 9.0, X libraies所在位置是

/usr/X11R6/lib
我make后，得到一下信息：
[root@localhost xmovie]# make
gcc -c -O2 -finline-functions -g -DMISSINGDEFS -D_POSIX_SOURCE -DUSEPRIVATE -D
INCL_FLOAT -Wimplicit -Wunused -Wmissing-prototypes  xmovie.c
gcc -c -O2 -finline-functions -g -DMISSINGDEFS -D_POSIX_SOURCE -DUSEPRIVATE -D
INCL_FLOAT -Wimplicit -Wunused -Wmissing-prototypes  control.c
gcc -c -O2 -finline-functions -g -DMISSINGDEFS -D_POSIX_SOURCE -DUSEPRIVATE -D
INCL_FLOAT -Wimplicit -Wunused -Wmissing-prototypes  scene.c
scene.c: In function `MotionUpdate':
scene.c:155: warning: passing arg 4 of `XpmWriteFileFromPixmap' makes integer  
from pointer without a cast
scene.c: In function `SceneSave':
scene.c:188: warning: passing arg 4 of `XpmWriteFileFromPixmap' makes integer  
from pointer without a cast
gcc -c -O2 -finline-functions -g -DMISSINGDEFS -D_POSIX_SOURCE -DUSEPRIVATE -D
INCL_FLOAT -Wimplicit -Wunused -Wmissing-prototypes  read.c
read.c: In function `SortData':
read.c:980: warning: passing arg 1 of `hpsort' from incompatible pointer type

read.c:980: warning: passing arg 4 of `hpsort' from incompatible pointer type

gcc -c -O2 -finline-functions -g -DMISSINGDEFS -D_POSIX_SOURCE -DUSEPRIVATE -D
INCL_FLOAT -Wimplicit -Wunused -Wmissing-prototypes  hpsort.c
hpsort.c:11: warning: no previous prototype for `hpsort'
hpsort.c: In function `hpsort':
hpsort.c:18: warning: implicit declaration of function `malloc'
hpsort.c:21: warning: implicit declaration of function `memcpy'
hpsort.c:42: warning: implicit declaration of function `free'
gcc -c -O2 -finline-functions -g -DMISSINGDEFS -D_POSIX_SOURCE -DUSEPRIVATE -D
INCL_FLOAT -Wimplicit -Wunused -Wmissing-prototypes  version.c
gcc -o xmovie -O2 -finline-functions -g  version.o xmovie.o control.o scene.o  
read.o hpsort.o -L/usr/X11R6/lib -lX11 -lXaw

可以看到上面出现了一些warning，请问这是什么原因？
谢谢