Define various symbols conditionally in shared libraries executables

[Wilco Dijkstra]

Hi Alan,

This commit (fd161d860f1df7140153eab4726705cc3e2727b0) caused lots of
failures on aarch64-none-elf. A typical test failure is like:

..binutils/ld/ld-new:built in linker script:160: syntax error

There are around 300 of these. Do you have an idea which builtin script this is?

Wilco