meson: Add LLVM bitcode emission for backend sources

Since generated backend sources may have their own compilation flags and
must also be included in the postgres.index.bc, the way to make it work
with current code was to create a new variable, called
`bc_generated_backend_sources`, which is a list of dictionaries, each
one having an optional 'additional_flags' and a `srclist` pointing to
the list of custom_target generated sources.

An example of a possible structure of bitcode_modules which is processed
by the main meson llvm bitcode emission file
src/backend/jit/llvm/bitcode/meson.build:
```
bitcode_modules = [
  {
    'name': 'postgres',
    'target': postgres_lib,
    'src_file': backend_sources,
    'gen_srcfiles': [
      {
        'additional_flags': [
          '-I/path/postgresl/src/backend/parser',
          '-I/path/postgresl/build/src/backend/parser',
        ],
        'srcfiles': [
                <custom_target for scan.c>,
                <custom_target for gram.c>
        ]
      }
    ]
  }
]
```

Author: Diego Fronza <[email protected]>
Author: Nazir Bilal Yavuz <[email protected]>
Discussion: https://postgr.es/m/206b001d-1884-4081-bd02-bed5c92f02ba%40eisentraut.org

Author: nbyavuz

src/backend/bootstrap/meson.build

@@ -13,13 +13,15 @@ bootscanner = custom_target('bootscanner',
 )
 generated_sources += bootscanner
 boot_parser_sources += bootscanner
+bc_generated_backend_sources += {'srcfiles': [bootscanner]}
 
 bootparse = custom_target('bootparse',
   input: 'bootparse.y',
   kwargs: bison_kw,
 )
 generated_sources += bootparse.to_list()
 boot_parser_sources += bootparse
+bc_generated_backend_sources += {'srcfiles': [bootparse[0]]}
 
 boot_parser = static_library('boot_parser',
   boot_parser_sources,

src/backend/meson.build

@@ -5,6 +5,7 @@ backend_sources = []
 backend_link_with = [pgport_srv, common_srv]
 
 generated_backend_sources = []
+bc_generated_backend_sources = []
 post_export_backend_sources = []
 
 subdir('access')
@@ -144,6 +145,7 @@ bitcode_modules += {
   'name': 'postgres',
   'target': postgres_lib,
   'srcfiles': backend_sources,
+  'gen_sources': bc_generated_backend_sources,
 }
 
 pg_mod_c_args = cflags_mod

src/backend/parser/meson.build

@@ -42,6 +42,14 @@ backend_parser = custom_target('gram',
 generated_sources += backend_parser.to_list()
 parser_sources += backend_parser
 
+bc_generated_backend_sources += {
+  'additional_flags': [
+    '-I@0@'.format(meson.current_build_dir()),
+    '-I@0@'.format(meson.current_source_dir()),
+  ],
+  'srcfiles': [backend_scanner, backend_parser[0]],
+}
+
 parser = static_library('parser',
   parser_sources,
   dependencies: [backend_code],

src/backend/replication/meson.build

@@ -19,13 +19,15 @@ repl_scanner = custom_target('repl_scanner',
 )
 generated_sources += repl_scanner
 repl_parser_sources += repl_scanner
+bc_generated_backend_sources += {'srcfiles': [repl_scanner]}
 
 repl_gram = custom_target('repl_gram',
   input: 'repl_gram.y',
   kwargs: bison_kw,
 )
 generated_sources += repl_gram.to_list()
 repl_parser_sources += repl_gram
+bc_generated_backend_sources += {'srcfiles': [repl_gram[0]]}
 
 syncrep_scanner = custom_target('syncrep_scanner',
   input: 'syncrep_scanner.l',
@@ -34,13 +36,15 @@ syncrep_scanner = custom_target('syncrep_scanner',
 )
 generated_sources += syncrep_scanner
 repl_parser_sources += syncrep_scanner
+bc_generated_backend_sources += {'srcfiles': [syncrep_scanner]}
 
 syncrep_gram = custom_target('syncrep_gram',
   input: 'syncrep_gram.y',
   kwargs: bison_kw,
 )
 generated_sources += syncrep_gram.to_list()
 repl_parser_sources += syncrep_gram
+bc_generated_backend_sources += {'srcfiles': [syncrep_gram[0]]}
 
 repl_parser = static_library('repl_parser',
   repl_parser_sources,

src/backend/utils/fmgr/meson.build

@@ -8,3 +8,4 @@ backend_sources += files(
 
 # fmgrtab.c
 generated_backend_sources += fmgrtab_target[2]
+bc_generated_backend_sources += {'srcfiles': [fmgrtab_target[2]]}