Git 2.16.2: Build failure linking static libcurl / static SSL

[Paul Smith <paul@mad-scientist.net>]

I'm compiling Git with my own static libcurl and my own static
LibreSSL.  They live in two different locations.

Building Curl with a pointer to my LibreSSL works fine, and compiling
Git works fine: the correct -I options are added to the compile line
when I configure with --with-openssl=/path/to/libressl/dist

However, linking fails to find the crypto and ssl libraries, because
the OPENSSLDIR lib directory is not added to the link line with -L. 
The link line in question is from Makefile:

  git-http-fetch$X: http.o http-walker.o http-fetch.o GIT-LDFLAGS $(GITLIBS)
        $(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
                $(CURL_LIBCURL) $(LIBS)
  git-http-push$X: http.o http-push.o GIT-LDFLAGS $(GITLIBS)
        $(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
                $(CURL_LIBCURL) $(EXPAT_LIBEXPAT) $(LIBS)

The OpenSSL libraries are included in CURL_LIBCURL, but the -L flags
are not:

        ifdef NEEDS_SSL_WITH_CURL
                CURL_LIBCURL += -lssl
                ifdef NEEDS_CRYPTO_WITH_SSL
                        CURL_LIBCURL += -lcrypto
                endif
        endif

This section needs to add in the OPENSSL_LINK variable, or maybe it has
to go directly in the git-http-fetch/push recipe, I'm not sure which is
appropriate.  There seems to be a lot of different variables that have
similar content, that maybe should be aligned (OPENSSL_LIBSSL,
OPENSSL_LINK, LIB_4_CRYPTO, CURL_LIBCURL, etc.)

But, the -L is definitely missing:

  gcc -g -O2 -I. -DGIT_HOST_CPU="\"x86_64\"" -DHAVE_ALLOCA_H -I/work/src/git/Linux-Release-make/dist/include -I/work/src/libressl/Linux-Release-make/dist/include -DNO_GETTEXT -DSHA1_DC -DSHA1DC_NO_STANDARD_INCLUDES -DSHA1DC_INIT_SAFE_HASH_DEFAULT=0 -DSHA1DC_CUSTOM_INCLUDE_SHA1_C="\"cache.h\"" -DSHA1DC_CUSTOM_INCLUDE_UBC_CHECK_C="\"git-compat-util.h\"" -pthread -DHAVE_PATHS_H -DHAVE_STRINGS_H -DHAVE_DEV_TTY -DHAVE_CLOCK_GETTIME -DHAVE_CLOCK_MONOTONIC -DHAVE_GETDELIM  -DFREAD_READS_DIRECTORIES -DNO_STRLCPY -DSHELL_PATH='"/bin/sh"' -DPAGER_ENV='"LESS=FRX LV=-c"' -o git-http-fetch   http.o http-walker.o http-fetch.o common-main.o \
        -L/work/src/git/Linux-Release-make/dist/lib -L/work/src/git/Linux-Release-make/dist/lib -lcurl -lssl -lcrypto -lidn libgit.a xdiff/lib.a  -lz -pthread -lrt
  ld: error: cannot find -lssl
  ld: error: cannot find -lcrypto

Note how the -I.../libressl/.../include option is present, but the
-L.../libressl/.../lib option is missing.