gdb: Use initializers in lambda captures unconditionally Initializer in lambda captures were introduced in C++14, and conditionally used in gdb/cp-support.c and gdb/dwarf2/cooked-index.c. Since C++17 is now required by GDB, use this feature unconditionally. Change-Id: I87a3d567941e5c71217538fa75c952e4d421fa1d