cmake: add pcre2 support

Fix one of the TODOs listed in the CMakeLists.txt by adding support
for building with pcre2.

As pcre2 doesn't provide cmake find module, we find it with pkgconf.
This patch also works with vcpkg on Windows, with pkgconf and pcre2
installed.

Pkgconf and pcre2 is detected automatically just like curl, expat
and iconv. The output of CMake indicates whether pcre2 is found.

Signed-off-by: Yuyi Wang <Strawberry_Str@hotmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/buildsystems/CMakeLists.txt

@@ -108,7 +108,6 @@ project(git
 
 #TODO gitk git-gui gitweb
 #TODO Enable NLS on windows natively
-#TODO Add pcre support
 
 #macros for parsing the Makefile for sources and scripts
 macro(parse_makefile_for_sources list_var regex)
@@ -160,6 +159,14 @@ if(NOT (WIN32 AND (CMAKE_C_COMPILER_ID STREQUAL "MSVC" OR CMAKE_C_COMPILER_ID ST
 	find_package(Intl)
 endif()
 
+find_package(PkgConfig)
+if(PkgConfig_FOUND)
+	pkg_check_modules(PCRE2 libpcre2-8)
+	if(PCRE2_FOUND)
+		add_compile_definitions(USE_LIBPCRE2)
+	endif()
+endif()
+
 if(NOT Intl_FOUND)
 	add_compile_definitions(NO_GETTEXT)
 	if(NOT Iconv_FOUND)
@@ -180,6 +187,9 @@ endif()
 if(Intl_FOUND)
 	include_directories(SYSTEM ${Intl_INCLUDE_DIRS})
 endif()
+if(PCRE2_FOUND)
+	include_directories(SYSTEM ${PCRE2_INCLUDE_DIRS})
+endif()
 
 
 if(WIN32 AND NOT MSVC)#not required for visual studio builds
@@ -700,6 +710,10 @@ endif()
 if(Iconv_FOUND)
 	target_link_libraries(common-main ${Iconv_LIBRARIES})
 endif()
+if(PCRE2_FOUND)
+	target_link_libraries(common-main ${PCRE2_LIBRARIES})
+	target_link_directories(common-main PUBLIC ${PCRE2_LIBRARY_DIRS})
+endif()
 if(WIN32)
 	target_link_libraries(common-main ws2_32 ntdll ${CMAKE_BINARY_DIR}/git.res)
 	add_dependencies(common-main git-rc)