Ruby

Add Clang compilation CI job on Ubuntu #8051

Job	Run time
C99_compile (4.0)	1m 13s
clang_compile (4.0)	1m 4s
clang_compile (head)	50s
C99_compile (head)	1m 0s
test (3.4, test)	2m 27s
test (4.0, typecheck_test)	1m 19s
test (asan-release, test)	7m 51s
test (4.0, test)	2m 21s
test (4.0, stdlib_test)	1m 57s
test (4.0, stdlib_test, --enable-frozen-string-literal)	2m 5s
test (4.0, test, --enable-frozen-string-literal)	2m 15s
test (head, stdlib_test rubocop)	1m 56s
test (3.3, test)	2m 29s
test (4.0, rubocop validate test_doc build test_generate_stdlib raap)	2m 38s
test (3.2, test)	2m 13s
test (head, test)	2m 25s
	36m 3s

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