REGEX is wrong for readelf used by cpack DEB generator

The following code is used to get the soversion.

string(REGEX MATCH "\\(SONAME\\)[^\n]*\\[([^\n]+)\\.so\\.([^\n]*)\\]" soname "${output}")

However this relies on gcc's readelf. LLVM has a slightly different version that doesn't have () around SONAME.

LLVM:
0x000000000000000e SONAME               Library soname: [libxxxxxx.so.3]

GCC:
0x000000000000000e (SONAME)             Library soname: [libxxxxxx.so.3]