update CHANGELOG, INSTALL and cross config for iOS

CHANGELOG

@@ -29,6 +29,7 @@
 
 * Pending changes since 16.1.3
 ** Enhancements
+- iOS support thanks to the help of P. Ruetz and gitlab user Whimse
 - hash-table may now have a custom equivalence predicate
 - ~make-load-form-with-slots~ works for structs even if slot names are not interned
 - ~ext:weak-pointer-value~ returns two values (value and its presence)

INSTALL

@@ -65,5 +65,61 @@ MacPort command:
 #+BEGIN_SRC shell-script
   sudo port select --set gcc none
 #+END_SRC
-   
+
 Hint provided by Pascal J. Bourguignon.
+
+
+* Cross-compile for the iOS platform
+1. Build the host ECL
+   #+BEGIN_SRC shell-script
+     ./configure --prefix=`pwd`/ecl-iOS-host --disable-c99complex
+     make -j9
+     make install
+     rm -r build
+     export ECL_TO_RUN=`pwd`/ecl-iOS-host/bin/ecl
+   #+END_SRC
+2. Configure the toolchain
+   #+BEGIN_SRC shell-script
+     export IOS_VERSION_MIN="8.0"
+     export IOS_SDK_DIR="`xcode-select --print-path`/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/"
+
+     export CC="clang"
+     export CXX="clang++"
+
+     export CFLAGS="-arch arm64 -miphoneos-version-min=${IOS_VERSION_MIN} -isysroot ${IOS_SDK_DIR}"
+     export CFLAGS="$CFLAGS -pipe -Wno-trigraphs -Wreturn-type -Wunused-variable"
+     export CFLAGS="$CFLAGS -fpascal-strings -fasm-blocks -fmessage-length=0 -fvisibility=hidden"
+     export CFLAGS="$CFLAGS -O2 -DNO_ASM"
+
+     export LD="ld"
+     export LDFLAGS="-arch arm64 -pipe -std=c99 -gdwarf-2 -isysroot ${IOS_SDK_DIR}"
+     export LIBS="-framework Foundation"
+   #+END_SRC
+3. Build and install the target library
+   #+BEGIN_SRC shell-script
+     export CFLAGS="$CFLAGS -DECL_C_COMPATIBLE_VARIADIC_DISPATCH -DGC_DISABLE_INCREMENTAL -DECL_RWLOCK"
+     export CXXFLAGS="$CFLAGS"
+     ./configure --host=aarch64-apple-darwin \
+                 --prefix=`pwd`/ecl-iOS \
+                 --disable-c99complex \
+                 --disable-shared \
+                 --with-cross-config=`pwd`/src/util/iOS-arm64.cross_config
+     make -j9
+     make install
+   #+END_SRC
+4. Library and assets in the ecl-iOS directory are ready to run on
+   the iOS system.
+
+** Using ECL on iOS
+
+The Boehm-Demers-Weiser garbage collector cannot find the stack base
+automatically on iOS. Therefore, this has to be specified manually. In
+the main function, before calling cl_boot, add e.g. (see the garbage
+collector documentation for more details):
+#+BEGIN_SRC C
+  const int size = 256;
+  char* ecl_argv[size];
+  GC_allow_register_threads();
+  GC_register_my_thread((const struct GC_stack_base*)ecl_argv);
+  GC_stackbottom = (char*)(ecl_argv + size - 1);
+#+END_SRC

src/util/iOS-arm64.cross_config

@@ -0,0 +1,21 @@
+ECL_STACK_DIR=down
+CL_FIXNUM_TYPE=long
+CL_FIXNUM_BITS=64
+CL_FIXNUM_MAX=2305843009213693951L
+CL_FIXNUM_MIN=-2305843009213693952L
+CL_INT_BITS=32
+CL_LONG_BITS=64
+ECL_BIGENDIAN=no
+ECL_NEWLINE=LF
+ECL_FILE_CNT=0
+ECL_STDINT_HEADER="#include <stdint.h>"
+ECL_UINT8_T=uint8_t
+ECL_UINT16_T=uint16_t
+ECL_UINT32_T=uint32_t
+ECL_UINT64_T=uint64_t
+ECL_INT8_T=int8_t
+ECL_INT16_T=int16_t
+ECL_INT32_T=int32_t
+ECL_INT64_T=int64_t
+ECL_LONG_LONG_BITS=no
+ECL_WORKING_ENVIRON=yes