Comment 1 for bug 230460

Ok, after some tests, here's the answer to what -Bsymbolic-functions does:

Let's assume libxfont1 defines a function
extern void foo(void);
and also uses this function.

With -Bsymbolic-functions, the call inside libxfont1 will always resolve to the function located in libxfont1.
Without the linker option, it's possible for a program (or library) linking against libxfont1 to override foo(), by specifying an own version of it. Then the call inside libxfont1 will get resolved to the version defined in the program instead.