Missing debug symbols for some extern functions

[jdm]

STR:

• Build Servo
• Open NodeListBinding.rs, find getOwnPropertyDescriptor and set a breakpoint inside of it by line number (it can't be found by name)
• Run ./servo ../src/test/content/test_node_normalize.html
• Attempt to investigate any variables, receive messages like $1 = {<text gnu-indirect-function variable, no debug info>} 0x3a5de84590 <strchr>. Notice the missing arguments information and mangled function name.

[jdm]

cc @michaelwoerister

[jdm]

#22071 is probably a better description of this problem.