Get tests working

[certik]

With lfortran/lfortran#7808 and this PR, the assert library now compiles and tests run:

(fpm) ~/repos/assert(fix-test)$ fpm build --compiler=lfortran --flag "--cpp" --verbose
 + mkdir -p build/dependencies
 <INFO> BUILD_NAME: build/lfortran
 <INFO> COMPILER:  lfortran
 <INFO> C COMPILER:  cc
 <INFO> CXX COMPILER: cc
 <INFO> COMPILER OPTIONS:   --cpp
 <INFO> C COMPILER OPTIONS:
 <INFO> CXX COMPILER OPTIONS:
 <INFO> LINKER OPTIONS:
 <INFO> INCLUDE DIRECTORIES:  [././include]
 + mkdir -p build/lfortran_DD9E02EB65F839BA
 + mkdir -p build/lfortran_73DB93E530B7A2CC
[  0%]        assert_subroutine_m.F90
 + mkdir -p build/lfortran_DD9E02EB65F839BA/assert/
 + lfortran -c ././src/assert/assert_subroutine_m.F90   --cpp -I././include -J build/lfortran_DD9E02EB65F839BA -Ibuild/lfortran_DD9E02EB65F839BA -o build/lfortran_DD9E02EB65F839BA/assert/src_assert_assert_subroutine_m.F90.o
[ 10%]        assert_subroutine_m.F90  done.
[ 10%] fortran_stringify_integer_m.f9
 + lfortran -c ././src/assert/fortran_stringify_integer_m.f90   --cpp -I././include -J build/lfortran_DD9E02EB65F839BA -Ibuild/lfortran_DD9E02EB65F839BA -o build/lfortran_DD9E02EB65F839BA/assert/src_assert_fortran_stringify_integer_m.f90.o
[ 20%] fortran_stringify_integer_m.f9  done.
[ 20%]                   assert_m.f90
 + lfortran -c ././src/assert_m.f90   --cpp -I././include -J build/lfortran_DD9E02EB65F839BA -Ibuild/lfortran_DD9E02EB65F839BA -o build/lfortran_DD9E02EB65F839BA/assert/src_assert_m.f90.o
[ 30%]                   assert_m.f90  done.
[ 30%]                    libassert.a
 + ar -rs build/lfortran_DD9E02EB65F839BA/assert/libassert.a build/lfortran_DD9E02EB65F839BA/assert/src_assert_m.f90.o build/lfortran_DD9E02EB65F839BA/assert/src_assert_assert_subroutine_m.F90.o build/lfortran_DD9E02EB65F839BA/assert/src_assert_fortran_stringify_integer_m.f90.o
ar: creating archive build/lfortran_DD9E02EB65F839BA/assert/libassert.a
warning: /Library/Developer/CommandLineTools/usr/bin/ranlib: archive library: build/lfortran_DD9E02EB65F839BA/assert/libassert.a the table of contents is empty (no object file members in the library define global symbols)
[ 40%]                    libassert.a  done.
[ 40%]          simple-assertions.f90
 + lfortran -c example/simple-assertions.f90   --cpp -I././include -J build/lfortran_DD9E02EB65F839BA -Ibuild/lfortran_DD9E02EB65F839BA -o build/lfortran_DD9E02EB65F839BA/assert/example_simple-assertions.f90.o
[ 50%]          simple-assertions.f90  done.
[ 50%]           invoke-via-macro.F90
 + lfortran -c example/invoke-via-macro.F90   --cpp -I././include -J build/lfortran_DD9E02EB65F839BA -Ibuild/lfortran_DD9E02EB65F839BA -o build/lfortran_DD9E02EB65F839BA/assert/example_invoke-via-macro.F90.o
[ 60%]           invoke-via-macro.F90  done.
[ 60%]            false-assertion.F90
 + lfortran -c example/false-assertion.F90   --cpp -I././include -J build/lfortran_DD9E02EB65F839BA -Ibuild/lfortran_DD9E02EB65F839BA -o build/lfortran_DD9E02EB65F839BA/assert/example_false-assertion.F90.o
[ 70%]            false-assertion.F90  done.
[ 70%]              simple-assertions
 + mkdir -p build/lfortran_73DB93E530B7A2CC/example/
 + lfortran    --cpp -I././include  build/lfortran_DD9E02EB65F839BA/assert/example_simple-assertions.f90.o  build/lfortran_DD9E02EB65F839BA/assert/libassert.a -o build/lfortran_73DB93E530B7A2CC/example/simple-assertions
[ 80%]              simple-assertions  done.
[ 80%]               invoke-via-macro
 + lfortran    --cpp -I././include  build/lfortran_DD9E02EB65F839BA/assert/example_invoke-via-macro.F90.o  build/lfortran_DD9E02EB65F839BA/assert/libassert.a -o build/lfortran_73DB93E530B7A2CC/example/invoke-via-macro
[ 90%]               invoke-via-macro  done.
[ 90%]                false-assertion
 + lfortran    --cpp -I././include  build/lfortran_DD9E02EB65F839BA/assert/example_false-assertion.F90.o  build/lfortran_DD9E02EB65F839BA/assert/libassert.a -o build/lfortran_73DB93E530B7A2CC/example/false-assertion
[100%]                false-assertion  done.
[100%] Project compiled successfully.
(fpm) ~/repos/assert(fix-test)$ fpm test --compiler=lfortran --flag "--cpp"
test-assert-subroutine-normal-terminatidone.
test-assert-macro.F90                  done.
test-assert-subroutine-error-terminatiodone.
test-assert-subroutine-normal-terminatidone.
test-assert-macro                      done.
test-assert-subroutine-error-terminatiodone.
[100%] Project compiled successfully.

The assert subroutine
  passes on not error-terminating when assertion=.true.

The call_assert macro
  passes on not error-terminating when an assertion expression evaluating to .true. is the only argument
  passes on being removed by the preprocessor when ASSERTIONS is undefined

The call_assert_describe macro
  passes on not error-terminating when assertion = .true. and a description is present
  passes on being removed by the preprocessor when ASSERTIONS is undefined

The call_assert_* macros
  pass on invocation from a pure function

The assert subroutine
passes on error-terminating when assertion = .false.

[certik]

This workaround works because exit_status is already logged while doing the call execute_command_line(...).