If a function's address is taken, which means it may be called via a function pointer,
we need the function descriptor for it.
Otherwise, the function descriptor can be omitted for external symbols.
When generating XCOFF, the compiler generates a csect with an internal
name. Each function results in a label within the csect. This patch
replaces the internal name ".text" with an empty string "". This avoids
adding special code to handle a function text() in the source file, and
works better with some XCOFF tools that are confused when the csect and
the first function have the same address.
Reviewed By: hubert.reinterpretcast
Differential Revision: https://reviews.llvm.org/D154854
