Fix #16937; --clib option pass library name to backend C compiler correctly (#19754)

* Fix 16937: Make --clib option works

* Make tests/compiler/tcmdlineclib.nim works from any current dir

* Try to fix link error on macosx

* Add a comment to tests/compiler/tcmdlineclib.nims

Co-authored-by: Clay Sweetser <Varriount@users.noreply.github.com>

tests/compiler/samplelib.nim

@@ -0,0 +1,2 @@
+# Sample library used by tcmdlineclib.nim
+proc test(): int {.cdecl, exportc, dynlib.} = 123

tests/compiler/tcmdlineclib.nim

@@ -0,0 +1,3 @@
+proc test(): int {.importc, cdecl.}
+
+doAssert test() == 123

tests/compiler/tcmdlineclib.nims

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+import os
+
+selfExec "c --app:lib " & (projectDir() / "samplelib.nim")
+switch("clibdir", projectDir())
+--clib:samplelib
+
+# Make test executable can load sample shared library.
+# `-rpath` option doesn't work and ignored on Windows.
+# But the dll file in same directory as executable file is loaded.
+switch("passL", "-Wl,-rpath," & projectDir())