cross-compilers: allow individual configuration

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

.gitignore

@@ -17,9 +17,10 @@ a.out
 tcc_g
 tcc
 *-tcc
+libtcc*.def
 
-config.h
-config.mak
+config*.h
+config*.mak
 config.texi
 conftest*
 tags
@@ -29,13 +30,6 @@ tcc.pod
 tcc-doc.html
 tcc-doc.info
 
-lib/x86_64
-lib/i386
-lib/x86_64-win32
-lib/i386-win32
-lib/arm
-lib/arm64
-
 win32/doc
 win32/libtcc
 win32/lib/32
@@ -60,5 +54,3 @@ tests/libtcc_test
 tests/vla_test
 tests/hello
 tests/tests2/fred.txt
-
-libtcc*.def