collada-dom: adding libpcre dependency

Executing 'bitbake packagegroup-ros-world' shows the warning:
WARNING: QA Issue: collada-dom rdepends on libpcrecpp but its not a build dependency? [build-deps]

On a clean build, 'bitbake collada-dom' fails with:
| Linking CXX shared library libcollada-dom2.4-dp.so
...
| .../build/tmp-eglibc/sysroots/x86_64-linux/usr/libexec/x86_64-oe-linux/gcc/x86_64-oe-linux/4.9.1/ld: external-libs/pcre-8.02/libpcre_local.a(pcre_compile.c.o): relocation R_X86_64_32S against `.rodata' can not be used when making a shared object; recompile with -fPIC
| external-libs/pcre-8.02/libpcre_local.a: error adding symbols: Bad value
| collect2: error: ld returned 1 exit status
| make[2]: *** [dom/libcollada-dom2.4-dp.so.2.4.0] Error 1

This commits adds libpcre as dependency, and resolves the issue.