postgresql: move libecpq to lib output

This library is used by other packages, so should be in the lib output.

By removing unused sections, libecpg will not contain any references to other
outputs and thus does not increase the closure for the lib output anymore.
This will also help massively when splitting a dev output later.

As a side-effect, this also unbreaks pkgsMusl.postgresql_12_jit and
pkgsMusl.postgresql_13_jit. For, at least to me, unknown reasons, those build
fine now.

pkgs/servers/sql/postgresql/generic.nix

@@ -23,7 +23,7 @@ let
 
       # JIT
       , jitSupport
-      , nukeReferences, patchelf, llvmPackages
+      , nukeReferences, patchelf, llvmPackages, overrideCC
 
       # PL/Python
       , pythonSupport ? false
@@ -43,7 +43,16 @@ let
 
     pname = "postgresql";
 
-    stdenv' = if jitSupport then llvmPackages.stdenv else stdenv;
+    stdenv' =
+      # TODO: Change back to default stdenv for non-jit / isDarwin case
+      # once LTO works after #307880.
+      if jitSupport || stdenv.isDarwin then
+        overrideCC llvmPackages.stdenv (llvmPackages.stdenv.cc.override {
+          # LLVM bintools are not used by default, but are needed to make -flto work below.
+          bintools = llvmPackages.bintools;
+        })
+      else
+        stdenv;
   in stdenv'.mkDerivation (finalAttrs: {
     inherit version;
     pname = pname + lib.optionalString jitSupport "-jit";
@@ -53,10 +62,15 @@ let
       inherit hash;
     };
 
+    __structuredAttrs = true;
+
     hardeningEnable = lib.optionals (!stdenv'.cc.isClang) [ "pie" ];
 
     outputs = [ "out" "lib" "doc" "man" ];
     setOutputFlags = false; # $out retains configureFlags :-/
+    outputChecks.lib = {
+      disallowedReferences = [ "out" "doc" "man" ];
+    };
 
     buildInputs = [
       zlib
@@ -87,9 +101,21 @@ let
 
     buildFlags = [ "world" ];
 
-    # Makes cross-compiling work when xml2-config can't be executed on the host.
-    # Fixed upstream in https://github.com/postgres/postgres/commit/0bc8cebdb889368abdf224aeac8bc197fe4c9ae6
-    env.NIX_CFLAGS_COMPILE = lib.optionalString (olderThan "13") "-I${libxml2.dev}/include/libxml2";
+    # libpgcommon.a and libpgport.a contain all paths returned by pg_config and are linked
+    # into all binaries. However, almost no binaries actually use those paths. The following
+    # flags will remove unused sections from all shared libraries and binaries - including
+    # those paths. This avoids a lot of circular dependency problems with different outputs,
+    # and allows splitting them cleanly.
+    env.CFLAGS = "-fdata-sections -ffunction-sections"
+      + (if stdenv'.cc.isClang then " -flto" else " -fmerge-constants -Wl,--gc-sections")
+      + lib.optionalString stdenv'.isDarwin " -fuse-ld=lld"
+      # Makes cross-compiling work when xml2-config can't be executed on the host.
+      # Fixed upstream in https://github.com/postgres/postgres/commit/0bc8cebdb889368abdf224aeac8bc197fe4c9ae6
+      + lib.optionalString (olderThan "13") " -I${libxml2.dev}/include/libxml2";
+
+    # This could be removed once the upstream issue is resolved:
+    # https://postgr.es/m/flat/427c7c25-e8e1-4fc5-a1fb-01ceff185e5b%40technowledgy.de
+    configureFlagsArray = lib.optionalString (stdenv'.isDarwin && atLeast "16") "LDFLAGS_EX_BE=-Wl,-export_dynamic";
 
     configureFlags = [
       "--with-openssl"
@@ -124,6 +150,8 @@ let
       map fetchurl (lib.attrValues muslPatches)
     ) ++ lib.optionals stdenv'.isLinux  [
       (if atLeast "13" then ./patches/socketdir-in-run-13+.patch else ./patches/socketdir-in-run.patch)
+    ] ++ lib.optionals (stdenv'.isDarwin && olderThan "16") [
+      ./patches/export-dynamic-darwin-15-.patch
     ];
 
     installTargets = [ "install-world" ];
@@ -138,7 +166,6 @@ let
       ''
         moveToOutput "lib/libpgcommon*.a" "$out"
         moveToOutput "lib/libpgport*.a" "$out"
-        moveToOutput "lib/libecpg*" "$out"
 
         # Prevent a retained dependency on gcc-wrapper.
         substituteInPlace "$out/lib/pgxs/src/Makefile.global" --replace ${stdenv'.cc}/bin/ld ld
@@ -255,9 +282,7 @@ let
       # resulting LLVM IR isn't platform-independent this doesn't give you much.
       # In fact, I tried to test the result in a VM-test, but as soon as JIT was used to optimize
       # a query, postgres would coredump with `Illegal instruction`.
-      broken = (jitSupport && stdenv.hostPlatform != stdenv.buildPlatform)
-        # Allmost all tests fail FATAL errors for v12 and v13
-        || (jitSupport && stdenv.hostPlatform.isMusl && olderThan "14");
+      broken = jitSupport && stdenv.hostPlatform != stdenv.buildPlatform;
     };
   });
 

pkgs/servers/sql/postgresql/patches/export-dynamic-darwin-15-.patch

@@ -0,0 +1,13 @@
+See https://postgr.es/m/eb249761-56e2-4e42-a2c5-b9ae18c1ca1f%40technowledgy.de
+---
+--- a/src/makefiles/Makefile.darwin
++++ b/src/makefiles/Makefile.darwin
+@@ -5,6 +5,8 @@ DLSUFFIX = .so
+ # env var name to use in place of LD_LIBRARY_PATH
+ ld_library_path_var = DYLD_LIBRARY_PATH
+
++export_dynamic = -Wl,-export_dynamic
++
+ ifdef PGXS
+   BE_DLLLIBS = -bundle_loader $(bindir)/postgres
+ else