Fix use of '-rdynamic'

[jpereira]

The option should be informed to the linker.

[jpereira]

It fixes the below warnings.

clang -DHAVE_CONFIG_H -I.  -DNDEBUG  -pedantic -Wall -Wextra -std=c99 -D_XOPEN_SOURCE_EXTENDED -DSYSCONFDIR=\"/usr/local/etc\" -I"./linux" -rdynamic -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -g -O2 -MT linux/LinuxProcessList.o -MD -MP -MF $depbase.Tpo -c -o linux/LinuxProcessList.o linux/LinuxProcessList.c &&\
mv -f $depbase.Tpo $depbase.Po
clang: warning: argument unused during compilation: '-rdynamic' [-Wunused-command-line-argument]

[natoscott]

Merged here: htop-dev/htop@0622be6