Officially introduce amalgamated builds (#4416)

Remove redundancy between all-in-one and all-in-one-source builds
by keeping only the second, and adopt the more established term
"amalgamated" build for it. This change includes the following:

- Replace `ENABLE_ALL_IN_ONE` and `ENABLE_ALL_IN_ONE_SOURCE` cmake
  options with `ENABLE_AMALGAM` top-level option.
- Replace `--all-in-one` option of `build.py` helper with
  `--amalgam`.
- Merge the `srcmerger.py` and `srcgenerator.py` tool scripts into
  `amalgam.py` (with improvements).
- Update documentation.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

CMakeLists.txt

@@ -59,6 +59,7 @@ set(DOCTESTS                OFF CACHE BOOL "Build doc tests?")
 
 # Optional build settings
 set(BUILD_SHARED_LIBS  OFF CACHE BOOL "Build shared libraries?")
+set(ENABLE_AMALGAM     OFF CACHE BOOL "Enable amalgamated build?")
 set(ENABLE_LTO         ON  CACHE BOOL "Enable LTO build?")
 set(ENABLE_STRIP       ON  CACHE BOOL "Enable stripping all symbols from release binary?")
 
@@ -104,8 +105,10 @@ if(USING_TI)
 endif()
 
 if(USING_MSVC)
+  set(ENABLE_AMALGAM     ON) # FIXME: This should not be needed but right now it is. To be tracked down and followed up.
   set(ENABLE_STRIP       OFF)
 
+  set(ENABLE_AMALGAM_MESSAGE     " (FORCED BY COMPILER)")
   set(ENABLE_STRIP_MESSAGE       " (FORCED BY COMPILER)")
 endif()
 
@@ -121,6 +124,7 @@ message(STATUS "CMAKE_C_COMPILER_ID            " ${CMAKE_C_COMPILER_ID})
 message(STATUS "CMAKE_SYSTEM_NAME              " ${CMAKE_SYSTEM_NAME})
 message(STATUS "CMAKE_SYSTEM_PROCESSOR         " ${CMAKE_SYSTEM_PROCESSOR})
 message(STATUS "BUILD_SHARED_LIBS              " ${BUILD_SHARED_LIBS})
+message(STATUS "ENABLE_AMALGAM                 " ${ENABLE_AMALGAM} ${ENABLE_AMALGAM_MESSAGE})
 message(STATUS "ENABLE_LTO                     " ${ENABLE_LTO} ${ENABLE_LTO_MESSAGE})
 message(STATUS "ENABLE_STRIP                   " ${ENABLE_STRIP} ${ENABLE_STRIP_MESSAGE})
 message(STATUS "JERRY_VERSION                  " ${JERRY_VERSION})
@@ -247,8 +251,8 @@ if(DEFINED EXTERNAL_LINKER_FLAGS)
   jerry_add_link_flags(${EXTERNAL_LINKER_FLAGS})
 endif()
 
-# Used for placeholder to attach single source build targets
-add_custom_target(generate-single-source)
+# Used as placeholder to attach amalgamated build targets to
+add_custom_target(amalgam)
 
 # Jerry's libm
 if(JERRY_MATH)