Fix some errors when compiling C++ code

After more or less recent changes, several headers do not compile when
included by C++ code with default esp-idf SDK compiler flags.

These issues were introduced by:
- 320d476 (bitstring.h)
- f260b37 (globalcontext.h)
- 6816741 (intn.h)

Signed-off-by: Paul Guyot <pguyot@kallisys.net>

Author: pguyot

src/libAtomVM/bitstring.h

@@ -75,6 +75,8 @@ extern "C" {
 // these values are the same used from opcodes such as bs_get_utf16
 enum BitstringFlags
 {
+    // Big endian & unsigned are the default
+    BigEndianInteger = 0x0,
     LittleEndianInteger = 0x2,
     SignedInteger = 0x4,
     NativeEndianInteger = 0x10,
@@ -369,7 +371,7 @@ static inline bool bitstring_utf8_size(uint32_t c, size_t *out_size)
  * unicode character
  */
 static inline bool bitstring_utf16_size(uint32_t c, size_t *out_size) {
-    return bitstring_utf16_encode(c, NULL, 0, out_size);
+    return bitstring_utf16_encode(c, NULL, BigEndianInteger, out_size);
 }
 
 /**

src/libAtomVM/globalcontext.h

@@ -459,7 +459,7 @@ static inline bool globalcontext_is_term_equal_to_atom_string(GlobalContext *glo
  */
 static inline term globalcontext_make_atom(GlobalContext *glb, AtomString atom_string)
 {
-    return globalcontext_insert_atom_maybe_copy(glb, atom_string_data(atom_string), atom_string_len(atom_string), false);
+    return globalcontext_insert_atom_maybe_copy(glb, (const uint8_t *) atom_string_data(atom_string), atom_string_len(atom_string), false);
 }
 
 /**

src/libAtomVM/intn.h

@@ -405,7 +405,7 @@ size_t intn_sub_int64(int64_t num1, int64_t num2, intn_digit_t *out, intn_intege
  */
 static inline intn_integer_sign_t intn_muldiv_sign(intn_integer_sign_t s1, intn_integer_sign_t s2)
 {
-    return (intn_integer_sign_t) ((unsigned int) s1 ^ (unsigned int) s2) & IntNNegativeInteger;
+    return (intn_integer_sign_t) (((unsigned int) s1 ^ (unsigned int) s2) & IntNNegativeInteger);
 }
 
 /**