ninjabackend: Adding missing shell quotes for compiler arguments

Since trying to cross compile for Windows from Linux (WSL) and having
paths like this:

  '-L/mnt/c/Program Files (x86)/Microsoft Visual Studio/2017/\
    Community/VC/Tools/MSVC/14.15.26726/lib/x64'

I found that the spaces and brackets in the paths weren't properly
escaped by the Ninja backend.

mesonbuild/backend/ninjabackend.py

@@ -1473,7 +1473,7 @@ int dummy;
                     command_template = ' command = {executable} $ARGS {output_args} $in $LINK_ARGS {cross_args} $aliasing\n'
                 command = command_template.format(
                     executable=' '.join(compiler.get_linker_exelist()),
-                    cross_args=' '.join(cross_args),
+                    cross_args=' '.join([quote_func(i) for i in cross_args]),
                     output_args=' '.join(compiler.get_linker_output_args('$out'))
                 )
                 description = ' description = Linking target $out.\n'
@@ -1601,7 +1601,7 @@ rule FORTRAN_DEP_HACK%s
             command_template = ' command = {executable} $ARGS {cross_args} {output_args} {compile_only_args} $in\n'
         command = command_template.format(
             executable=' '.join([ninja_quote(i) for i in compiler.get_exelist()]),
-            cross_args=' '.join(compiler.get_cross_extra_flags(self.environment, False)) if is_cross else '',
+            cross_args=' '.join([quote_func(i) for i in compiler.get_cross_extra_flags(self.environment, False)]) if is_cross else '',
             output_args=' '.join(compiler.get_output_args('$out')),
             compile_only_args=' '.join(compiler.get_compile_only_args())
         )
@@ -1659,7 +1659,7 @@ rule FORTRAN_DEP_HACK%s
             command_template = ' command = {executable} $ARGS {cross_args} {dep_args} {output_args} {compile_only_args} $in\n'
         command = command_template.format(
             executable=' '.join([ninja_quote(i) for i in compiler.get_exelist()]),
-            cross_args=' '.join(cross_args),
+            cross_args=' '.join([quote_func(i) for i in cross_args]),
             dep_args=' '.join(quoted_depargs),
             output_args=' '.join(compiler.get_output_args('$out')),
             compile_only_args=' '.join(compiler.get_compile_only_args())
@@ -1703,7 +1703,7 @@ rule FORTRAN_DEP_HACK%s
             output = ' '.join(compiler.get_output_args('$out'))
         command = " command = {executable} $ARGS {cross_args} {dep_args} {output_args} {compile_only_args} $in\n".format(
             executable=' '.join(compiler.get_exelist()),
-            cross_args=' '.join(cross_args),
+            cross_args=' '.join([quote_func(i) for i in cross_args]),
             dep_args=' '.join(quoted_depargs),
             output_args=output,
             compile_only_args=' '.join(compiler.get_compile_only_args())