Android update and small improvements

-fixed code do cross compiling to android
-fixed build with GCC (workaround)
-added little benchmark
-several small fixes
-updated meson build (demos building, working with GCC, LDC and DMD)
-added some meson options
-added ImGUI bind for OpenGL3

compile_android.py

@@ -0,0 +1,78 @@
+import os
+import ntpath
+import sys
+
+def compile(sources, output):
+    files = []
+    # r=root, d=directories, f = files
+    for path in sources:
+        for r, d, f in os.walk(path):
+            for file in f:
+                if ntpath.basename(file) != 'win_dll.d':
+                    filename, file_extension = os.path.splitext(file)
+                    if file_extension == '.d' and filename != 'package':
+                        files.append(os.path.join(r, file))
+    
+    ldc_path = 'ldc'
+    if 'LDC' in os.environ:
+        ldc_path = os.environ['LDC']
+        
+    ldc_cmd = ldc_path + ' ' + ldc_flags + '-lib -mtriple=armv7-none-linux-androideabi -fvisibility=hidden -betterC -oq -od=obj/ --singleobj --of=' + output + ' '
+    
+    for path in sources:
+        ldc_cmd += '-I' + path + ' '
+        
+    for path in import_paths:
+        ldc_cmd += '-I' + path + ' '
+        
+    for f in files:
+        ldc_cmd += f + ' '
+
+    print(ldc_cmd)
+
+    if os.system(ldc_cmd):
+        exit(0)
+    print()
+
+clean = 0
+ldc_flags = ''
+import_paths = ['source','tests']
+build_tests = 0
+
+for arg in sys.argv[1:]:
+    if(arg == '-release'):
+        ldc_flags += '-release '
+    elif(arg == '-enable-inlining'):
+        ldc_flags += '-enable-inlining '
+    elif(arg == '-O3'):
+        ldc_flags += '-O3 '
+    elif(arg == '-O2'):
+        ldc_flags += '-O2 '
+    elif(arg == '-O1'):
+        ldc_flags += '-O1 '
+    elif(arg == '-O0'):
+        ldc_flags += '-O0 '
+    elif(arg == '-Os'):
+        ldc_flags += '-Os '
+    elif(arg == '-Oz'):
+        ldc_flags += '-Oz '
+    elif(arg == '-g'):
+        ldc_flags += '-g '
+    elif(arg == '-opt'):
+        ldc_flags += '-release -enable-inlining -O3 '
+    else:
+        print('unknown argument: ' + arg)
+        exit()
+    
+compile(['source'], 'ecs.a')
+
+#export LDC_LIBS=/path/to/your/ldc-build-runtime.tmp/lib/
+CC = os.environ['NDK'] + '/toolchains/llvm/prebuilt/linux-x86_64/bin/clang'
+TOOLCHAIN = os.environ['NDK'] + '/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64'
+SYSROOT = os.environ['NDK'] + '/platforms/android-21/arch-arm'
+LDC_LIBS = ''#os.environ['LDC_LIBS'] + '/libphobos2-ldc.a ' + os.environ['LDC_LIBS'] + '/libdruntime-ldc.a'
+
+os.system(CC + ' -Wl,-soname,libecs.so -shared --sysroot=' + SYSROOT + ' obj/*.o ' + LDC_LIBS + ' -lgcc -gcc-toolchain ' + TOOLCHAIN + 
+' -no-canonical-prefixes -fuse-ld=bfd -target armv7-none-linux-androideabi -fvisibility=hidden \
+-Wl,--gc-sections -Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,-z,noexecstack -Wl,-z,relro \
+-Wl,-z,now -mthumb -o libecs.so')