Return -DPIC with pkg-config --cflags alsa when appropriate

[afq984]

Some build systems (we are using bazel) do not define -DPIC when compiling position independent objects.

When building a alsa module, if PIC is not defined, global.h requires the presence of the snd_dlsym_start symbol, which is absent from libasound.so if alsa itself is built with -DPIC.

alsa-lib/include/global.h

Line 72 in 9447e57

extern struct snd_dlsym_link *snd_dlsym_start;

If the PIC macro is non-standard I would suggest exposing it via pkg-config so position independent alsa modules can pick up the flag and apply it to the alsa headers appropriately.

[perexg]

It's a third-party module ? This flag is set by configure (libtool) and it is not required for the standard alsa-lib apps (except the modules). I would suggest to add #define PIC 1 line to the third-party module source or build rules.

[afq984]

yeah we're building an alsa plugin for our audio server (CRAS). We currently add -DPIC to our build rules, and I'm wondering if it make sense for this to exposed from pkg-config.
If you think nothing needs to be changed feel free to close this, thanks!