apply linux notes from martins; simplify build.sh; simplify some linux layer code; fix incorrect linux api usage; get gcc builds up and running

src/base/base_core.h

@@ -287,7 +287,7 @@ CheckNil(nil,p) ? \
 # endif
 # define NO_ASAN __attribute__((no_sanitize("address")))
 #else
-# error "NO_ASAN is not defined for this compiler."
+# define NO_ASAN
 #endif
 
 #if ASAN_ENABLED

src/base/base_strings.c

@@ -1281,7 +1281,7 @@ utf16_decode(U16 *str, U64 max){
   result.codepoint = str[0];
   result.inc = 1;
   if (max > 1 && 0xD800 <= str[0] && str[0] < 0xDC00 && 0xDC00 <= str[1] && str[1] < 0xE000){
-    result.codepoint = ((str[0] - 0xD800) << 10) | (str[1] - 0xDC00) + 0x10000;
+    result.codepoint = ((str[0] - 0xD800) << 10) | ((str[1] - 0xDC00) + 0x10000);
     result.inc = 2;
   }
   return(result);