Link libintl in case of Alpine (#5731)

This delta detects Alpine Linux by using `uname -v` (kernel version)
and add the `libintl` in the linker list. This is because `gettext` is
not part of (per-installed in) Alpine Linux but available via the
package manager. To build CoreCLR, `gettext-dev` is one unlisted
per-requisite.

src/pal/src/CMakeLists.txt

@@ -2,6 +2,13 @@ cmake_minimum_required(VERSION 2.8.12.2)
 
 include_directories(SYSTEM /usr/local/include)
 
+# set kernel version to detect Alpine
+EXEC_PROGRAM(uname ARGS -v OUTPUT_VARIABLE CMAKE_SYSTEM_KERNEL_VERSION)
+string(FIND "${CMAKE_SYSTEM_KERNEL_VERSION}" "Alpine" PAL_SYSTEM_ALPINE)
+if(PAL_SYSTEM_ALPINE EQUAL -1)
+    unset(PAL_SYSTEM_ALPINE)
+endif()
+
 include(configure.cmake)
 
 project(coreclrpal)
@@ -245,6 +252,10 @@ if(CMAKE_SYSTEM_NAME STREQUAL Linux)
     find_library(UNWIND_ARCH NAMES unwind-x86_64)
   endif()
 
+  if(PAL_SYSTEM_ALPINE)
+    find_library(INTL intl)
+  endif()
+
   find_library(UNWIND NAMES unwind)
   find_library(UNWIND_GENERIC NAMES unwind-generic)
 
@@ -270,6 +281,10 @@ if(CMAKE_SYSTEM_NAME STREQUAL Linux)
     target_link_libraries(coreclrpal ${UNWIND_ARCH})
   endif(NOT UNWIND_ARCH STREQUAL UNWIND_ARCH-NOTFOUND)
 
+  if(NOT INTL STREQUAL INTL-NOTFOUND)
+    target_link_libraries(coreclrpal ${INTL})
+  endif(NOT INTL STREQUAL INTL-NOTFOUND)
+
 endif(CMAKE_SYSTEM_NAME STREQUAL Linux)
 
 if(CMAKE_SYSTEM_NAME STREQUAL NetBSD)