bash-4.2$ gcc -v main.c
Reading specs from /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/specs
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-slackware-linux/4.7.1/lto-wrapper
Target: x86_64-slackware-linux
Configured with: ../gcc-4.7.1/configure --prefix=/usr --libdir=/usr/lib64 --mandir=/usr/man --infodir=/usr/info --enable-shared --enable-bootstrap --enable-languages=ada,c,c++,fortran,go,java,lto,objc --enable-threads=posix --enable-checking=release --enable-objc-gc --with-system-zlib --with-python-dir=/lib64/python2.7/site-packages --disable-libunwind-exceptions --enable-__cxa_atexit --enable-libssp --enable-lto --with-gnu-ld --verbose --enable-java-home --with-java-home=/usr/lib64/jvm/jre --with-jvm-root-dir=/usr/lib64/jvm --with-jvm-jar-dir=/usr/lib64/jvm/jvm-exports --with-arch-directory=amd64 --with-antlr-jar=/slack/TMPTMPTMP/gcc-round-two/antlr-runtime-3.4.jar --enable-java-awt=gtk --disable-gtktest --disable-multilib --target=x86_64-slackware-linux --build=x86_64-slackware-linux --host=x86_64-slackware-linux
Thread model: posix
gcc version 4.7.1 (GCC) 
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-slackware-linux/4.7.1/cc1 -quiet -v main.c -quiet -dumpbase main.c -mtune=generic -march=x86-64 -auxbase main -version -o /tmp/ccwIjwU9.s
GNU C (GCC) version 4.7.1 (x86_64-slackware-linux)
        compiled by GNU C version 4.7.1, GMP version 5.0.5, MPFR version 3.1.0, MPC version 0.8.2
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../x86_64-slackware-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/include
 /usr/local/include
 /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/include-fixed
 /usr/include
End of search list.
GNU C (GCC) version 4.7.1 (x86_64-slackware-linux)
        compiled by GNU C version 4.7.1, GMP version 5.0.5, MPFR version 3.1.0, MPC version 0.8.2
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: d15405e407e9ac0241fcd0167b686d79
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
 /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../x86_64-slackware-linux/bin/as -v --64 -o /tmp/cc5XjsHB.o /tmp/ccwIjwU9.s
GNU assembler version 2.22.52.0.2 (x86_64-slackware-linux) using BFD version (Linux/GNU Binutils) 2.22.52.0.2.20120424
COMPILER_PATH=/usr/libexec/gcc/x86_64-slackware-linux/4.7.1/:/usr/libexec/gcc/x86_64-slackware-linux/4.7.1/:/usr/libexec/gcc/x86_64-slackware-linux/:/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/:/usr/lib64/gcc/x86_64-slackware-linux/:/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../x86_64-slackware-linux/bin/
LIBRARY_PATH=/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/:/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../x86_64-slackware-linux/lib/:/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-slackware-linux/4.7.1/collect2 --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../lib64/crt1.o /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../lib64/crti.o /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/crtbegin.o -L/usr/lib64/gcc/x86_64-slackware-linux/4.7.1 -L/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../x86_64-slackware-linux/lib -L/usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../.. /tmp/cc5XjsHB.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/crtend.o /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/../../../../lib64/crtn.o
/tmp/cc5XjsHB.o: In function `frequency_of_primes':
main.c:(.text+0x23): undefined reference to `sqrt'
collect2: error: ld returned 1 exit status