crda: fix compile warning on pcc for reglib for string.h

This fixes these compile warnings:

make -j5 -l4 UDEV_RULE_DIR=/lib/udev/rules.d
REG_BIN=/usr/lib64/crda/regulatory.bin USE_OPENSSL=1
CC=x86_64-pc-linux-gnu-gcc all_noverify V=1
x86_64-pc-linux-gnu-gcc -c  -Os -pipe -march=native
-frecord-gcc-switches -ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -o crda.o crda.c
x86_64-pc-linux-gnu-gcc -c  -Os -pipe -march=native
-frecord-gcc-switches -ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -o intersect.o
intersect.c
./utils/key2pub.py --ssl pubkeys/linville.key.pub.pem keys-ssl.c
x86_64-pc-linux-gnu-gcc -c  -Os -pipe -march=native
-frecord-gcc-switches -ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -o
print-regdom.o print-regdom.c
x86_64-pc-linux-gnu-gcc -c  -Os -pipe -march=native
-frecord-gcc-switches -ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -o regdbdump.o
regdbdump.c
x86_64-pc-linux-gnu-gcc -c  -Os -pipe -march=native
-frecord-gcc-switches -ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -o reglib.o
reglib.c
reglib.c: In function ‘country2rd’:
reglib.c:213:2: warning: implicit declaration of function ‘memset’
[-Wimplicit-function-declaration]
reglib.c:213:2: warning: incompatible implicit declaration of built-in
function ‘memset’ [enabled by default]
reglib.c: In function ‘reglib_get_rd_alpha2’:
reglib.c:344:3: warning: implicit declaration of function ‘memcmp’
[-Wimplicit-function-declaration]
x86_64-pc-linux-gnu-gcc -Os -pipe -march=native -frecord-gcc-switches
-ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -Wl,-O1
-Wl,--as-needed -Wl,--hash-style=gnu -o crda reglib.o crda.o `pkg-config
--libs openssl` -lnl-genl-3 -lnl-3   `pkg-config --libs libnl-3.0`
x86_64-pc-linux-gnu-gcc -Os -pipe -march=native -frecord-gcc-switches
-ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -Wl,-O1
-Wl,--as-needed -Wl,--hash-style=gnu -o intersect reglib.o intersect.o
print-regdom.o `pkg-config --libs openssl`
x86_64-pc-linux-gnu-gcc -Os -pipe -march=native -frecord-gcc-switches
-ggdb -Wall -g -DUSE_OPENSSL
-DPUBKEY_DIR=\"/etc/wireless-regdb/pubkeys\" `pkg-config --cflags
openssl` -DCONFIG_LIBNL30 `pkg-config --cflags libnl-3.0` -Wl,-O1
-Wl,--as-needed -Wl,--hash-style=gnu -o regdbdump reglib.o regdbdump.o
print-regdom.o `pkg-config --libs openssl`

Reported-by: Richard Farina <sidhayn@gmail.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>