toolchain-external: clarify the comment about *-gcc-ar... LTO wrappers

# Build toolchain wrapper for preprocessor, C and C++ compiler and setup

# symlinks for everything else. Skip gdb symlink when we are building our

# own gdb to prevent two gdb's in output/host/usr/bin.

# When the link-time-optimization flag '-flto' is used, then the compiler

# and binutils have to support lto. ar/ranlib need to be called with the

# lto plugin. The wrappers *-gcc-ar and *-gcc-ranlib provided by GCC could

# be used as drop-ins for ar/runlib when Makefiles are used which do not

# pass the lto arguments.

# The LTO support in gcc creates wrappers for ar, ranlib and nm which load

# the lto plugin. These wrappers are called *-gcc-ar, *-gcc-ranlib, and

# *-gcc-nm and should be used instead of the real programs when -flto is

# used. However, we should not add the toolchain wrapper for them, and they

# match the *cc-* pattern. Therefore, an additional case is added for *-ar,

# *-ranlib and *-nm.

define TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER

	$(Q)$(call MESSAGE,"Building ext-toolchain wrapper")

	$(Q)mkdir -p $(HOST_DIR)/usr/bin