Add an explicit test for rules with no inputs.
# Check that a command with no inputs runs properly on the first invocation,
# even if the output already exists.
#
# RUN: rm -rf %t.build
# RUN: mkdir -p %t.build
# RUN: cp %s %t.build/build.ninja
# RUN: touch %t.build/output
# RUN: %{llbuild} ninja build --no-parallel --chdir %t.build &> %t1.out
# RUN: %{FileCheck} --check-prefix CHECK-FIRST --input-file %t1.out %s
#
# CHECK-FIRST: [1] date > output

# Running again should do nothing.
#
# RUN: %{llbuild} ninja build --no-parallel --chdir %t.build &> %t2.out
# RUN: %{FileCheck} --check-prefix CHECK-SECOND --input-file %t2.out %s
#
# CHECK-SECOND-NOT: date

rule DATE
     command = date > ${out}

build output: DATE