Fix make shell detection

[Peter0x44]

Fixes #6135.

The Makefiles assume Windows means cmd, but GNU Make can select sh
instead. This causes make clean to use the wrong shell commands.

Detect the recipe shell using echo "test": cmd preserves the quotes,
while sh removes them. Apply this to the library, examples and tools,
and remove the forced cmd shell from library cleanup. Explicit
PLATFORM_SHELL overrides remain supported.

Also fix Win32 clean recipe indentation and,
pass rlparser's recursive make variables as command-line arguments
so those calls work under both cmd and sh.

[emecdelam]

For curiosity, are there any reasons to use echo "test" instead of just finding the executable? something like

ifeq ($(OS),Windows_NT)
    ifeq ($(findstring sh.exe,$(SHELL)),sh.exe)
        DETECTED_SHELL := sh
    else
        DETECTED_SHELL := cmd
    endif
else
    DETECTED_SHELL := sh
endif

[Peter0x44]

Actually, my blogpost is a little wrong on this point. Make DOES report sh.exe in SHELL (it's not unset), but it's not consistent.

This is maybe a GNU make bug, but if you run make without an sh.exe on your PATH it will still report that it using sh (despite that it is NOT). Probably could be patched, but these buggy makes are of course going to be very widespread.

I still think it's the correct approach for this PR.

[Peter0x44]

   Configuration         $(SHELL)       $(shell echo "test")
  ━━━━━━━━━━━━━━━━━━━━  ━━━━━━━━━━━━━  ━━━━━━━━━━━━━━━━━━━━━━
   sh on PATH            C:/…/sh.exe    test
  ────────────────────  ─────────────  ──────────────────────
   No sh on PATH         sh.exe         "test"
  ────────────────────  ─────────────  ──────────────────────
   Explicit SHELL=sh     sh             test
  ────────────────────  ─────────────  ──────────────────────
   Explicit SHELL=cmd    cmd            "test"

[raysan5]

@Peter0x44 thanks for the review and the explanation!