Use a real linker arg in 'test cases/common/177 initial c_args'

`-Dtest_harmless_but_useless_link_arg` won't actually do anything
without anything to preprocess, but least it is valid for GCC and MSVC,
and won't be caused by anything else.

test cases/common/177 initial c_args/meson.build

@@ -3,5 +3,5 @@ project('options', 'c')
 # Test passing c_args and c_link_args options from the command line.
 assert(get_option('c_args') == ['-funroll-loops'],
        'Incorrect value for c_args option.')
-assert(get_option('c_link_args') == ['-random_linker_option'],
+assert(get_option('c_link_args') == ['-Dtest_harmless_but_useless_link_arg'],
        'Incorrect value for c_link_args option.')

test cases/common/177 initial c_args/test_args.txt

@@ -1,4 +1,4 @@
 # This file is not read by meson itself, but by the test framework.
 # It is not possible to pass arguments to meson from a file.
 ['-Dc_args=-march=native', '-Dc_args=-funroll-loops',
- '-Dc_link_args=-random_linker_option']
+ '-Dc_link_args=-Dtest_harmless_but_useless_link_arg']