Try dropping both U_COMMON_API and U_EXPORT2 for toUCharPtr

source/common/unicode/char16ptr.h

diff --git a/source/common/unicode/char16ptr.h b/source/common/unicode/char16ptr.h
index 7174235..3066f00 100644
--- a/source/common/unicode/char16ptr.h
+++ b/source/common/unicode/char16ptr.h
@@ -241,7 +241,7 @@
  * @return p as const UChar *
  * @draft ICU 59
  */
-inline U_COMMON_API const UChar* U_EXPORT2 toUCharPtr(const char16_t *p) {
+inline const UChar* toUCharPtr(const char16_t *p) {
 #ifdef U_ALIASING_BARRIER
     U_ALIASING_BARRIER(p);
 #endif
@@ -255,7 +255,7 @@
  * @return p as UChar *
  * @draft ICU 59
  */
-inline U_COMMON_API UChar* U_EXPORT2 toUCharPtr(char16_t *p) {
+inline UChar* toUCharPtr(char16_t *p) {
 #ifdef U_ALIASING_BARRIER
     U_ALIASING_BARRIER(p);
 #endif
@@ -269,7 +269,7 @@
  * @return p as const OldUChar *
  * @draft ICU 59
  */
-inline U_COMMON_API const OldUChar* U_EXPORT2 toOldUCharPtr(const char16_t *p) {
+inline const OldUChar* toOldUCharPtr(const char16_t *p) {
 #ifdef U_ALIASING_BARRIER
     U_ALIASING_BARRIER(p);
 #endif
@@ -283,7 +283,7 @@
  * @return p as OldUChar *
  * @draft ICU 59
  */
-inline U_COMMON_API OldUChar* U_EXPORT2 toOldUCharPtr(char16_t *p) {
+inline OldUChar* toOldUCharPtr(char16_t *p) {
 #ifdef U_ALIASING_BARRIER
     U_ALIASING_BARRIER(p);
 #endif