Comments only, no change to functionality

tcc.h:
* cleanup struct 'Sym'
* include some 'Attributes' into 'Sym'
* in turn get rid of VT_IM/EXPORT, VT_WEAK
* re-number VT_XXX flags
* replace some 'long' function args by 'int'

tccgen.c:
* refactor parse_btype()

- 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"
  7443db0d5f841b81a55e918bf8c228dd20f9ddb2
  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

* tccgen: re-allow long double constants for x87 cross
  sizeof (long double) may be 12 or 16 depending on host platform
  (i386/x86_64 on unix/windows).
  Except that it's 8 if the host is on windows and not gcc
  was used to compile tcc.

* win64: fix builtin_va_start after VT_REF removal
  See also a8b83ce43a95fa519dacfe7690a3a0098af7909c

* tcctest.c: remove outdated limitation for ll-bitfield test
  It always worked, there is no reason why it should not work
  in future.

* libtcc1.c: exclude long double conversion on ARM

* Makefile: remove CFLAGS from link recipes

* lib/Makefile: use target DEFINES as passed from main Makefile

* lib/armflush.c lib/va_list.c: factor out from libtcc1.c

* arm-gen.c: disable "depreciated" warnings for now

since configure supports only native configuration
a file 'cross-tcc.mak' needs to be created manually.
It is included in the Makefile if present.

# ----------------------------------------------------
# Example config-cross.mak:
#
# windows -> i386-linux cross-compiler
# (it expects the linux files in <prefix>/i386-linux)

ROOT-i386 = {B}/i386-linux
CRT-i386 = $(ROOT-i386)/usr/lib
LIB-i386 = $(ROOT-i386)/lib:$(ROOT-i386)/usr/lib
INC-i386 = {B}/lib/include:$(ROOT-i386)/usr/include
DEF-i386 += -D__linux__

# ----------------------------------------------------

Also:
- use libtcc1-<target>.a instead of directories
- add dummy arm assembler
- remove include dependencies from armeabi.c/lib-arm64.c
- tccelf/ld_add_file: add SYSROOT (when defined) to absolute
  filenames coming from ld-scripts

- tccgen.c/tcc.h: allow function declaration after use:
      int f() { return g(); }
      int g() { return 1; }
  may be a warning but not an error
  see also 76cb1144ef91924c53c57ea71e6f67ce73ce1cc6

- tccgen.c: redundant code related to inline functions removed
  (functions used anywhere have sym->c set automatically)

- tccgen.c: make 32bit llop non-equal test portable
  (probably not on C67)

- dynarray_add: change prototype to possibly avoid aliasing
  problems or at least warnings

- lib/alloca*.S: ".section .note.GNU-stack,"",%progbits" removed
  (has no effect)

- tccpe: set SizeOfCode field (for correct upx decompression)

- libtcc.c: fixed alternative -run invocation
      tcc "-run -lxxx ..." file.c
  (meant to load the library after file).
  Also supported now:
      tcc files ... options ... -run @ arguments ...

tccgen.c: remove any 'nocode_wanted' checks, except in
- greloca(), disables output elf symbols and relocs
- get_reg(), will return just the first suitable reg)
- save_regs(), will do nothing

Some minor adjustments were made where nocode_wanted is set.

xxx-gen.c: disable code output directly where it happens
in functions:
- g(), output disabled
- gjmp(), will do nothing
- gtst(), dto.

C standard specifies that array should be declared with a non null size
or with * for standard array. Declaration of relocs_info in tcc.h was
not respecting this rule. This commit add a R_NUM macro that maps to the
R_<ARCH>_NUM macros and declare relocs_info using it. This commit also
moves all linker-related macros from <arch>-gen.c files to <arch>-link.c
ones.