[meson] Provide Language-specific Linker Definitions

This is a new feature of meson v0.53.1 which chooses the linker in a
language-specific manner. We just set the linker for C and C++ to
explicitly be riscv32-unknown-elf-ld, the linker we normally use.

In the clang builds, this will be passed with `clang -fuse-ld=<path>`
which should work correctly, but uses the clang driver to establish all
the right arguments to pass down to the linker.

Signed-off-by: Sam Elliott <selliott@lowrisc.org>

generate-clang-meson-cross-file.sh

@@ -62,6 +62,8 @@ c = '${toolchain_dest}/bin/${toolchain_target}-clang'
 cpp = '${toolchain_dest}/bin/${toolchain_target}-clang++'
 ar = '${toolchain_dest}/bin/${toolchain_target}-ar'
 ld = '${toolchain_dest}/bin/${toolchain_target}-ld'
+c_ld = '${toolchain_dest}/bin/${toolchain_target}-ld'
+cpp_ld = '${toolchain_dest}/bin/${toolchain_target}-ld'
 objdump = '${toolchain_dest}/bin/${toolchain_target}-objdump'
 objcopy = '${toolchain_dest}/bin/${toolchain_target}-objcopy'
 strip = '${toolchain_dest}/bin/${toolchain_target}-strip'

generate-gcc-meson-cross-file.sh

@@ -61,6 +61,8 @@ c = '${toolchain_dest}/bin/${toolchain_target}-gcc'
 cpp = '${toolchain_dest}/bin/${toolchain_target}-g++'
 ar = '${toolchain_dest}/bin/${toolchain_target}-ar'
 ld = '${toolchain_dest}/bin/${toolchain_target}-ld'
+c_ld = '${toolchain_dest}/bin/${toolchain_target}-ld'
+cpp_ld = '${toolchain_dest}/bin/${toolchain_target}-ld'
 objdump = '${toolchain_dest}/bin/${toolchain_target}-objdump'
 objcopy = '${toolchain_dest}/bin/${toolchain_target}-objcopy'
 strip = '${toolchain_dest}/bin/${toolchain_target}-strip'