gccrs: Add execution test cases

This is similar to the compile/torture/*.rs test cases, but all of these are
dg-execute testcases. They are compiled, linked and executed by default. These
testcases are also compiled with the matrix of torture options.

The only caveat here is that gccrs does not currently support the main shim,
so we have a C-style main function here returning zero which is not proper Rust
code.

	gcc/testsuite/
	* rust/execute/torture/block_expr1.rs: New.
	* rust/execute/torture/builtin_macro_cfg.rs: New.
	* rust/execute/torture/builtin_macro_concat.rs: New.
	* rust/execute/torture/builtin_macro_env.rs: New.
	* rust/execute/torture/builtin_macro_include_bytes.rs: New.
	* rust/execute/torture/builtin_macro_include_str.rs: New.
	* rust/execute/torture/builtin_macro_line.rs: New.
	* rust/execute/torture/builtin_macros1.rs: New.
	* rust/execute/torture/builtin_macros3.rs: New.
	* rust/execute/torture/cfg1.rs: New.
	* rust/execute/torture/cfg2.rs: New.
	* rust/execute/torture/cfg3.rs: New.
	* rust/execute/torture/cfg4.rs: New.
	* rust/execute/torture/cfg5.rs: New.
	* rust/execute/torture/coercion1.rs: New.
	* rust/execute/torture/coercion2.rs: New.
	* rust/execute/torture/const_fold1.rs: New.
	* rust/execute/torture/const_fold2.rs: New.
	* rust/execute/torture/copy_nonoverlapping1.rs: New.
	* rust/execute/torture/empty_main.rs: New.
	* rust/execute/torture/execute.exp: New.
	* rust/execute/torture/exit_error.rs: New.
	* rust/execute/torture/extern_mod4.rs: New.
	* rust/execute/torture/func1.rs: New.
	* rust/execute/torture/helloworld1.rs: New.
	* rust/execute/torture/helloworld2.rs: New.
	* rust/execute/torture/include.txt: New.
	* rust/execute/torture/index1.rs: New.
	* rust/execute/torture/issue-1120.rs: New.
	* rust/execute/torture/issue-1133.rs: New.
	* rust/execute/torture/issue-1198.rs: New.
	* rust/execute/torture/issue-1231.rs: New.
	* rust/execute/torture/issue-1232.rs: New.
	* rust/execute/torture/issue-1249.rs: New.
	* rust/execute/torture/issue-1436.rs: New.
	* rust/execute/torture/issue-1496.rs: New.
	* rust/execute/torture/issue-647.rs: New.
	* rust/execute/torture/issue-845.rs: New.
	* rust/execute/torture/issue-851.rs: New.
	* rust/execute/torture/issue-858.rs: New.
	* rust/execute/torture/issue-976.rs: New.
	* rust/execute/torture/issue-995.rs: New.
	* rust/execute/torture/macros1.rs: New.
	* rust/execute/torture/macros10.rs: New.
	* rust/execute/torture/macros11.rs: New.
	* rust/execute/torture/macros12.rs: New.
	* rust/execute/torture/macros13.rs: New.
	* rust/execute/torture/macros14.rs: New.
	* rust/execute/torture/macros16.rs: New.
	* rust/execute/torture/macros17.rs: New.
	* rust/execute/torture/macros18.rs: New.
	* rust/execute/torture/macros19.rs: New.
	* rust/execute/torture/macros2.rs: New.
	* rust/execute/torture/macros20.rs: New.
	* rust/execute/torture/macros21.rs: New.
	* rust/execute/torture/macros22.rs: New.
	* rust/execute/torture/macros23.rs: New.
	* rust/execute/torture/macros24.rs: New.
	* rust/execute/torture/macros25.rs: New.
	* rust/execute/torture/macros26.rs: New.
	* rust/execute/torture/macros27.rs: New.
	* rust/execute/torture/macros28.rs: New.
	* rust/execute/torture/macros29.rs: New.
	* rust/execute/torture/macros3.rs: New.
	* rust/execute/torture/macros30.rs: New.
	* rust/execute/torture/macros31.rs: New.
	* rust/execute/torture/macros4.rs: New.
	* rust/execute/torture/macros5.rs: New.
	* rust/execute/torture/macros6.rs: New.
	* rust/execute/torture/macros7.rs: New.
	* rust/execute/torture/macros8.rs: New.
	* rust/execute/torture/macros9.rs: New.
	* rust/execute/torture/match1.rs: New.
	* rust/execute/torture/match2.rs: New.
	* rust/execute/torture/match3.rs: New.
	* rust/execute/torture/match_bool1.rs: New.
	* rust/execute/torture/match_byte1.rs: New.
	* rust/execute/torture/match_char1.rs: New.
	* rust/execute/torture/match_int1.rs: New.
	* rust/execute/torture/match_loop1.rs: New.
	* rust/execute/torture/match_range1.rs: New.
	* rust/execute/torture/match_range2.rs: New.
	* rust/execute/torture/match_tuple1.rs: New.
	* rust/execute/torture/method1.rs: New.
	* rust/execute/torture/method2.rs: New.
	* rust/execute/torture/method3.rs: New.
	* rust/execute/torture/method4.rs: New.
	* rust/execute/torture/mod1.rs: New.
	* rust/execute/torture/modules/mod.rs: New.
	* rust/execute/torture/operator_overload_1.rs: New.
	* rust/execute/torture/operator_overload_10.rs: New.
	* rust/execute/torture/operator_overload_11.rs: New.
	* rust/execute/torture/operator_overload_12.rs: New.
	* rust/execute/torture/operator_overload_2.rs: New.
	* rust/execute/torture/operator_overload_3.rs: New.
	* rust/execute/torture/operator_overload_4.rs: New.
	* rust/execute/torture/operator_overload_5.rs: New.
	* rust/execute/torture/operator_overload_6.rs: New.
	* rust/execute/torture/operator_overload_7.rs: New.
	* rust/execute/torture/operator_overload_8.rs: New.
	* rust/execute/torture/operator_overload_9.rs: New.
	* rust/execute/torture/slice-magic.rs: New.
	* rust/execute/torture/slice-magic2.rs: New.
	* rust/execute/torture/slice1.rs: New.
	* rust/execute/torture/str-layout1.rs: New.
	* rust/execute/torture/str-zero.rs: New.
	* rust/execute/torture/trait1.rs: New.
	* rust/execute/torture/trait10.rs: New.
	* rust/execute/torture/trait11.rs: New.
	* rust/execute/torture/trait12.rs: New.
	* rust/execute/torture/trait13.rs: New.
	* rust/execute/torture/trait2.rs: New.
	* rust/execute/torture/trait3.rs: New.
	* rust/execute/torture/trait4.rs: New.
	* rust/execute/torture/trait5.rs: New.
	* rust/execute/torture/trait6.rs: New.
	* rust/execute/torture/trait7.rs: New.
	* rust/execute/torture/trait8.rs: New.
	* rust/execute/torture/trait9.rs: New.
	* rust/execute/torture/transmute1.rs: New.
	* rust/execute/torture/wrapping_op1.rs: New.
	* rust/execute/torture/wrapping_op2.rs: New.
	* rust/execute/xfail/macro1.rs: New.

Co-authored-by: Arthur Cohen <arthur.cohen@embecosm.com>
Co-authored-by: Thomas Schwinge <thomas@codesourcery.com>
Co-authored-by: Mark Wielaard <mark@klomp.org>
Co-authored-by: Marc Poulhiès <dkm@kataplop.net>