Add debuginfo build target

In the webinar we are currently producing on debugging openssl
applications, we talk about ways to allow debugable binaries without
having to ship all the debug DWARF information to production systems.

Add an optional target to do that DWARF separation to aid users

Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25174)

Configurations/00-base-templates.conf

@@ -78,6 +78,7 @@ my %targets=(
         AR              => "ar",
         ARFLAGS         => "qc",
         CC              => "cc",
+        OBJCOPY         => "objcopy",
         bin_cflags      =>
             sub {
                 my @flags = ();

Configurations/unix-Makefile.tmpl

@@ -373,6 +373,7 @@ CFLAGS={- join(' ', @{$config{CFLAGS}}) -}
 CXXFLAGS={- join(' ', @{$config{CXXFLAGS}}) -}
 LDFLAGS= {- join(' ', @{$config{LDFLAGS}}) -}
 EX_LIBS= {- join(' ', @{$config{LDLIBS}}) -}
+OBJCOPY={- $config{OBJCOPY} -}
 
 MAKEDEPEND={- $config{makedepcmd} -}
 
@@ -533,6 +534,11 @@ LANG=C
 {- dependmagic('build_programs', 'Build the openssl executables and scripts'); -}: build_programs_nodep
 
 all: build_sw {- "build_docs" if !$disabled{docs}; -} ## Build software and documentation
+debuginfo: $(SHLIBS)
+	@set -e; for i in $(SHLIBS); do \
+		$(OBJCOPY) --only-keep-debug $$i $$i.debug; \
+		$(OBJCOPY) --strip-debug --add-gnu-debuglink=$$i.debug $$i; \
+	done;
 
 ##@ Documentation
 build_generated_pods: $(GENERATED_PODS)

Configure

@@ -758,6 +758,7 @@ my %user = (
     RANLIB      => env('RANLIB'),
     RC          => env('RC') || env('WINDRES'),
     RCFLAGS     => [ env('RCFLAGS') || () ],
+    OBJCOPY     => undef,
     RM          => undef,
    );
 # Info about what "make variables" may be prefixed with the cross compiler

INSTALL.md

@@ -1676,6 +1676,12 @@ described here.  Examine the Makefiles themselves for the full list.
     build_docs
                    Build all documentation components.
 
+    debuginfo
+                    On unix platforms, this target can be used to create .debug
+                    libraries, which separate the DWARF information in the
+                    shared library ELF files into a separate file for use
+                    in post-mortem (core dump) debugging
+
     clean
                    Remove all build artefacts and return the directory to a "clean"
                    state.