configure: --config-musl/-uClibc switch & misc cleanups

- configure:
  - add --config-uClibc,-musl switch and suggest to use
    it if uClibc/musl is detected
  - make warning options magic clang compatible
  - simplify (use $confvars instead of individual options)
- Revert "Remove some unused-parameter lint"
  7443db0d5f
  rather use -Wno-unused-parameter (or just not -Wextra)
- #ifdef functions that are unused on some targets
- tccgen.c: use PTR_SIZE==8 instead of (X86_64 || ARM64)
- tccpe.c: fix some warnings
- integrate dummy arm-asm better

tcctools.c

@@ -104,7 +104,6 @@ ST_FUNC int tcc_tool_ar(TCCState *s1, int argc, char **argv)
     const char *ops_conflict = "habdioptxN";  // unsupported but destructive if ignored.
     int verbose = 0;
 
-    (void) s1;  /* not used */
     i_lib = 0; i_obj = 0;  // will hold the index of the lib and first obj
     for (i = 1; i < argc; i++) {
         const char *a = argv[i];
@@ -322,7 +321,6 @@ ST_FUNC int tcc_tool_impdef(TCCState *s1, int argc, char **argv)
     p = NULL;
     v = 0;
 
-    (void) s1;  /* not used */
     for (i = 1; i < argc; ++i) {
         const char *a = argv[i];
         if ('-' == a[0]) {
@@ -435,7 +433,6 @@ the_end:
 
 ST_FUNC void tcc_tool_cross(TCCState *s, char **argv, int option)
 {
-    (void) s;  (void) argv;  /* not used */
     tcc_error("-m%d not implemented.", option);
 }
 
@@ -489,7 +486,6 @@ ST_FUNC void tcc_tool_cross(TCCState *s, char **argv, int target)
     char *a0 = argv[0];
     int prefix = tcc_basename(a0) - a0;
 
-    (void) s;  /* not used */
     snprintf(program, sizeof program,
         "%.*s%s"
 #ifdef TCC_TARGET_PE