Ruby

add `extern "C"` wrapping to `rbs.h` when using C++ #7861

Job	Run time
C99_compile (head)	1m 9s
C99_compile (4.0)	1m 13s
test (3.4, test)	2m 41s
test (head, test)	2m 23s
test (4.0, typecheck_test)	1m 19s
test (4.0, stdlib_test, --enable-frozen-string-literal)	2m 2s
test (3.3, test)	3m 7s
test (4.0, stdlib_test)	2m 14s
test (3.2, test)	2m 33s
test (4.0, rubocop validate test_doc build test_generate_stdlib raap)	3m 16s
test (head, stdlib_test rubocop)	2m 9s
test (4.0, test, --enable-frozen-string-literal)	2m 26s
test (asan-release, test)	8m 37s
test (4.0, test)	2m 52s
	38m 1s

Provide feedback