The test suite contains multiple instances of determining the target's
endianness with GDB's "show endian" command. This patch replaces these by
an invocation of a new convenience proc 'get_endianness'.
gdb/testsuite/ChangeLog:
* lib/gdb.exp (get_endianness): New proc.
* gdb.arch/aarch64-fp.exp: Use it.
* gdb.arch/altivec-regs.exp: Likewise.
* gdb.arch/e500-regs.exp: Likewise.
* gdb.arch/vsx-regs.exp: Likewise.
* gdb.base/dump.exp: Likewise.
* gdb.base/funcargs.exp: Likewise.
* gdb.base/gnu_vector.exp: Likewise.
* gdb.dwarf2/formdata16.exp: Likewise.
* gdb.dwarf2/implptrpiece.exp: Likewise.
* gdb.dwarf2/nonvar-access.exp: Likewise.
* gdb.python/py-inferior.exp: Likewise.
* gdb.trace/unavailable-dwarf-piece.exp: Likewise.