Add some negative test coverage for malformed -Clink-self-contained flags

Author: jieyouxu

tests/ui/linking/link-self-contained-malformed.invalid_modifier.stderr

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+error: incorrect value `*lld` for codegen option `link-self-contained` - one of: `y`, `yes`, `on`, `n`, `no`, `off`, or a list of enabled (`+` prefix) and disabled (`-` prefix) components: `crto`, `libc`, `unwind`, `linker`, `sanitizers`, `mingw` was expected
+

tests/ui/linking/link-self-contained-malformed.no_value.stderr

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+error: incorrect value `` for codegen option `link-self-contained` - one of: `y`, `yes`, `on`, `n`, `no`, `off`, or a list of enabled (`+` prefix) and disabled (`-` prefix) components: `crto`, `libc`, `unwind`, `linker`, `sanitizers`, `mingw` was expected
+

tests/ui/linking/link-self-contained-malformed.rs

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+//! Check that malformed `-Clink-self-contained` invocations are properly rejected.
+
+//@ revisions: no_value
+//@[no_value] compile-flags: -Clink-self-contained=
+//[no_value]~? ERROR incorrect value `` for codegen option `link-self-contained`
+
+//@ revisions: invalid_modifier
+//@[invalid_modifier] compile-flags: -Clink-self-contained=*lld
+//[invalid_modifier]~? ERROR incorrect value `*lld` for codegen option `link-self-contained`
+
+//@ revisions: unknown_value
+//@[unknown_value] compile-flags: -Clink-self-contained=unknown
+//[unknown_value]~? ERROR incorrect value `unknown` for codegen option `link-self-contained`
+
+//@ revisions: unknown_modifier_value
+//@[unknown_modifier_value] compile-flags: -Clink-self-contained=-unknown
+//[unknown_modifier_value]~? ERROR incorrect value `-unknown` for codegen option `link-self-contained`
+
+//@ revisions: unknown_boolean
+//@[unknown_boolean] compile-flags: -Clink-self-contained=maybe
+//[unknown_boolean]~? ERROR incorrect value `maybe` for codegen option `link-self-contained`
+
+fn main() {}

tests/ui/linking/link-self-contained-malformed.unknown_boolean.stderr

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+error: incorrect value `maybe` for codegen option `link-self-contained` - one of: `y`, `yes`, `on`, `n`, `no`, `off`, or a list of enabled (`+` prefix) and disabled (`-` prefix) components: `crto`, `libc`, `unwind`, `linker`, `sanitizers`, `mingw` was expected
+

tests/ui/linking/link-self-contained-malformed.unknown_modifier_value.stderr

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+error: incorrect value `-unknown` for codegen option `link-self-contained` - one of: `y`, `yes`, `on`, `n`, `no`, `off`, or a list of enabled (`+` prefix) and disabled (`-` prefix) components: `crto`, `libc`, `unwind`, `linker`, `sanitizers`, `mingw` was expected
+

tests/ui/linking/link-self-contained-malformed.unknown_value.stderr

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+error: incorrect value `unknown` for codegen option `link-self-contained` - one of: `y`, `yes`, `on`, `n`, `no`, `off`, or a list of enabled (`+` prefix) and disabled (`-` prefix) components: `crto`, `libc`, `unwind`, `linker`, `sanitizers`, `mingw` was expected
+