icu: fix potential UB in DangiCalendar

Method `getDangiCalZoneAstroCalc` is used to calculate an argument for
base class constructor when it is not built yet. Fortunately, it does not
use class fields - let's make it static to use it before class
initialization legitimately.

Closes tarantool/security#96

NO_TEST=no behaviour changes
NO_CHANGELOG=no behaviour changes
NO_DOC=no behaviour changes

static-build/cmake/AddDependencyProjects.cmake

@@ -118,6 +118,7 @@ ExternalProject_Add(icu
     PATCH_COMMAND patch -d <SOURCE_DIR> -p1 -i "${PATCHES_DIR}/icu-tarantool-security-45.patch"
     COMMAND       patch -d <SOURCE_DIR> -p1 -i "${PATCHES_DIR}/icu-tarantool-security-59.patch"
     COMMAND       patch -d <SOURCE_DIR> -p1 -i "${PATCHES_DIR}/icu-tarantool-security-61.patch"
+    COMMAND       patch -d <SOURCE_DIR> -p1 -i "${PATCHES_DIR}/icu-tarantool-security-96.patch"
 )
 set(TARANTOOL_DEPENDS icu ${TARANTOOL_DEPENDS})
 

static-build/patches/icu-tarantool-security-96.patch

+diff --git a/source/i18n/dangical.cpp b/source/i18n/dangical.cpp
+index 234c44b..f5343d0 100644
+--- a/source/i18n/dangical.cpp
++++ b/source/i18n/dangical.cpp
+@@ -136,7 +136,7 @@ static void U_CALLCONV initDangiCalZoneAstroCalc(UErrorCode &status) {
+     ucln_i18n_registerCleanup(UCLN_I18N_DANGI_CALENDAR, calendar_dangi_cleanup);
+ }
+ 
+-const TimeZone* DangiCalendar::getDangiCalZoneAstroCalc(UErrorCode &status) const {
++const TimeZone* DangiCalendar::getDangiCalZoneAstroCalc(UErrorCode &status) {
+     umtx_initOnce(gDangiCalendarInitOnce, &initDangiCalZoneAstroCalc, status);
+     return gDangiCalendarZoneAstroCalc;
+ }
+diff --git a/source/i18n/dangical.h b/source/i18n/dangical.h
+index 128f3af..e240272 100644
+--- a/source/i18n/dangical.h
++++ b/source/i18n/dangical.h
+@@ -74,7 +74,7 @@ class DangiCalendar : public ChineseCalendar {
+ 
+  private:
+ 
+-  const TimeZone* getDangiCalZoneAstroCalc(UErrorCode &status) const;
++  static const TimeZone* getDangiCalZoneAstroCalc(UErrorCode &status);
+ 
+   // UObject stuff
+  public: