Have libgit2 use our curl.

Enforce curl as a dependency for the libgit2 build.
Fix the libgit2 clean target
Build curl only on linux and osx.
Add pkg-config to build dependencies in README.md. Required to detect curl in libgit2 build.

(cherry picked from commit 3687527)
ref #17783

README.md

@@ -263,6 +263,7 @@ Building Julia requires that the following software be installed:
 - **[patch]**                   — for modifying source code.
 - **[cmake]**                   — needed to build `libgit2`.
 - **[openssl]**                 — needed for HTTPS support in `libgit2` on Linux, install via `apt-get install libssl-dev` or `yum install openssl-devel`.
+- **[pkg-config]**              - needed to build libgit2 correctly, especially for proxy support
 
 Julia uses the following external libraries, which are automatically downloaded (or in a few cases, included in the Julia source repository) and then compiled from source the first time you run `make`:
 
@@ -326,6 +327,7 @@ For a longer overview of Julia's dependencies, see these [slides](https://github
 [openssl]:      https://www.openssl.org
 [libssh2]:      https://www.libssh2.org
 [mbedtls]:      https://tls.mbed.org/
+[pkg-config]:   https://www.freedesktop.org/wiki/Software/pkg-config/
 
 <a name="System-Provided-Libraries">
 ### System Provided Libraries

contrib/windows/msys_build.sh

@@ -181,6 +181,7 @@ echo 'override LIBLAPACKNAME = $(LIBBLASNAME)' >> Make.user
 echo 'override STAGE1_DEPS = libuv' >> Make.user
 echo 'override STAGE2_DEPS = utf8proc' >> Make.user
 echo 'override STAGE3_DEPS = ' >> Make.user
+echo 'override STAGE4_DEPS = ' >> Make.user
 
 if [ -n "$USEMSVC" ]; then
   # Openlibm doesn't build well with MSVC right now

deps/Makefile

@@ -171,12 +171,14 @@ ifeq ($(USE_SYSTEM_LIBSSH2), 0)
 STAGE2_DEPS += libssh2
 endif
 
+ifneq ($(OS), WINNT)
 ifeq ($(USE_SYSTEM_CURL), 0)
-STAGE2_DEPS += curl
+STAGE3_DEPS += curl
+endif
 endif
 
 ifeq ($(USE_SYSTEM_LIBGIT2), 0)
-STAGE3_DEPS += libgit2
+STAGE4_DEPS += libgit2
 endif
 
 ifeq ($(USE_SYSTEM_MPFR), 0)
@@ -215,7 +217,7 @@ endif
 
 ## Common build target prefixes
 
-DEP_LIBS := $(STAGE1_DEPS) $(STAGE2_DEPS) $(STAGE3_DEPS)
+DEP_LIBS := $(STAGE1_DEPS) $(STAGE2_DEPS) $(STAGE3_DEPS) $(STAGE4_DEPS)
 
 default: install | $(build_prefix)
 get: $(addprefix get-, $(DEP_LIBS))

deps/libgit2.mk

@@ -19,6 +19,8 @@ else
 LIBGIT2_OPTS += -DBUILD_CLAR=OFF -DDLLTOOL=`which $(CROSS_COMPILE)dlltool`
 LIBGIT2_OPTS += -DCMAKE_FIND_ROOT_PATH=/usr/$(XC_HOST) -DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY
 endif
+else
+LIBGIT2_OPTS += -DCURL_INCLUDE_DIRS=$(build_includedir) -DCURL_LIBRARIES="-L$(build_shlibdir) -lcurl"
 endif
 
 ifeq ($(OS),Linux)
@@ -44,6 +46,9 @@ $(SRCDIR)/srccache/$(LIBGIT2_SRC_DIR)/libgit2-openssl-hang.patch-applied: | $(SR
 ifeq ($(OS),Linux)
 $(BUILDDIR)/$(LIBGIT2_SRC_DIR)/Makefile: $(SRCDIR)/srccache/$(LIBGIT2_SRC_DIR)/libgit2-require-openssl.patch-applied $(SRCDIR)/srccache/$(LIBGIT2_SRC_DIR)/libgit2-openssl-hang.patch-applied
 endif
+ifneq ($(OS),WINNT)
+$(BUILDDIR)/$(LIBGIT2_SRC_DIR)/Makefile: $(CURL_OBJ_TARGET)
+endif
 $(BUILDDIR)/$(LIBGIT2_SRC_DIR)/Makefile: $(SRCDIR)/srccache/$(LIBGIT2_SRC_DIR)/CMakeLists.txt $(SRCDIR)/srccache/$(LIBGIT2_SRC_DIR)/libgit2-ssh.patch-applied $(SRCDIR)/srccache/$(LIBGIT2_SRC_DIR)/libgit2-agent-nonfatal.patch-applied $(LIBSSH2_OBJ_TARGET)
 	mkdir -p $(dir $@)
 	cd $(dir $@) && \
@@ -73,14 +78,14 @@ ifeq ($(OS),Linux)
 	for LIB in libssl libcrypto; do \
 		LIB_PATH=$$(echo "$$LIBGIT_LIBS" | grep "$$LIB"); \
 		echo "LIB_PATH for $$LIB: $$LIB_PATH"; \
-		[ ! -z "$$LIB_PATH" ] && cp -v "$$LIB_PATH" $(build_shlibdir); \
+		[ ! -z "$$LIB_PATH" ] && cp -v -f "$$LIB_PATH" $(build_shlibdir); \
 	done
 endif
 	touch -c $@
 
 clean-libgit2:
 	-$(MAKE) -C $(BUILDDIR)/$(LIBGIT2_SRC_DIR) clean
-	-rm -f $(LIBGIT2_OBJ_TARGET)
+	-rm -f $(build_shlibdir)/libgit2* $(build_shlibdir)/libssl* $(build_shlibdir)/libcrypto*
 
 get-libgit2: $(LIBGIT2_SRC_FILE)
 configure-libgit2: $(BUILDDIR)/$(LIBGIT2_SRC_DIR)/Makefile