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>

compiler/commands.nim

@@ -803,7 +803,7 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
   of "clib":
     expectArg(conf, switch, arg, pass, info)
     if pass in {passCmd2, passPP}:
-      conf.cLinkedLibs.add processPath(conf, arg, info).string
+      conf.cLinkedLibs.add arg
   of "header":
     if conf != nil: conf.headerFile = arg
     incl(conf.globalOptions, optGenIndex)

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

@@ -0,0 +1,10 @@
+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())