Fix darwin build.

To fix darwin build, only use lld on linux.

Bug: 171348143
Test: run build.py.
Change-Id: Ica5a2ef86907406b2c0fe57ad7ddac81eb8fa705

Author: yabinc

config_toml.py

@@ -63,18 +63,20 @@ def host_config(target):
             else:
                 sysroot_flags = ""
 
+            ld_option = '-fuse-ld=lld' if build_platform.system() == 'linux' else ''
+
             with open(wrapper_name, 'w') as f:
                 f.write("""\
 #!/bin/sh
-{real_cc} $* -fuse-ld=lld --target={target} {sysroot_flags}
-""".format(real_cc=cc, target=target, sysroot_flags=sysroot_flags))
+{real_cc} $* {ld_option} --target={target} {sysroot_flags}
+""".format(real_cc=cc, ld_option=ld_option, target=target, sysroot_flags=sysroot_flags))
 
             with open(cxx_wrapper_name, 'w') as f:
                 f.write("""\
 #!/bin/sh
-{real_cxx} -I{cxxstd} $* -fuse-ld=lld --target={target} {sysroot_flags} {cxx_linker_flags} \
+{real_cxx} -I{cxxstd} $* {ld_option} --target={target} {sysroot_flags} {cxx_linker_flags} \
         -stdlib=libc++
-""".format(real_cxx=cxx, target=target, sysroot_flags=sysroot_flags,
+""".format(real_cxx=cxx, ld_option=ld_option, target=target, sysroot_flags=sysroot_flags,
            cxxstd=cxxstd,
            cxx_linker_flags=cxx_linker_flags))