pidgin/pidgin

Use LT_LIB_M to determine if we need to link to the math library and link Pidgin to the X11 libraries

Gentoo ran into an issue with the gold linker without -lm. The original patch
and work came from Justin Lechner. https://bugs.gentoo.org/386079

Gentoo also ran into an issue with X11_LIBS not being added to pidgin. This
should already be implicit everywhere except for homebrew which patches X11
out of their build. Original patch/work came from and. https://bugs.gentoo.org/500762

Testing Done:
Installed and ran locally.

Reviewed at https://reviews.imfreedom.org/r/608/
#error "This is file is not a valid C code"
/* This file contains some of the macros from other header files as
function declarations. This does not make sense in C, but it
provides type information for the dbus-analyze-functions.py
program, which makes these macros callable by DBUS. */
/* blist.h */
gboolean PURPLE_BLIST_NODE_IS_CHAT(PurpleBlistNode *node);
gboolean PURPLE_BLIST_NODE_IS_BUDDY(PurpleBlistNode *node);
gboolean PURPLE_BLIST_NODE_IS_CONTACT(PurpleBlistNode *node);
gboolean PURPLE_BLIST_NODE_IS_GROUP(PurpleBlistNode *node);
gboolean PURPLE_BUDDY_IS_ONLINE(PurpleBuddy *buddy);
gboolean PURPLE_BLIST_NODE_HAS_FLAG(PurpleBlistNode *node, int flags);
gboolean PURPLE_BLIST_NODE_SHOULD_SAVE(PurpleBlistNode *node);
/* connection.h */
gboolean PURPLE_CONNECTION_IS_CONNECTED(PurpleConnection *connection);
gboolean PURPLE_CONNECTION_IS_VALID(PurpleConnection *connection);
/* conversation.h */
PurpleConvIm *PURPLE_CONV_IM(const PurpleConversation *conversation);
PurpleConvIm *PURPLE_CONV_CHAT(const PurpleConversation *conversation);