Fine-tune build scripts and better documentation.

"make google/protobuf/stubs/pbconfig.h" was added in hope of addressing
the issue that when you "make protoc" from a freshly checked out
project, pbconfig.h will be reported missing. However, the trick doesn't
seem to work. Instead, add instructions in the document to work the issue
around.

Also document why MSYS2 cannot be used for publishing protoc.

protoc-artifacts/README.md

@@ -22,6 +22,20 @@ The scripts only work under Unix-like environments, e.g., Linux, MacOSX, and
 Cygwin or MinGW for Windows. Please see ``README.md`` of the Protobuf project
 for how to set up the build environment.
 
+## Building from a freshly checked-out source
+
+If you just checked out the Protobuf source from github, you need to
+generate the configure script. You also need to build the full project
+first to generate `pbconfig.h` which would otherwise be reported
+missing when you build protoc in the later steps. This needs to be
+done only once.
+
+Under the protobuf project directory:
+
+```
+$ ./autogen.sh && ./configure && make
+```
+
 ## To install artifacts locally
 The following command will install the ``protoc`` artifact to your local Maven repository.
 ```
@@ -43,7 +57,7 @@ Frequently used values are:
 - ``os.detected.name``: ``linux``, ``osx``, ``windows``.
 - ``os.detected.arch``: ``x86_32``, ``x86_64``
 
-For example, MingGW32 only ships with 32-bit compilers, but you can still build
+For example, MinGW32 only ships with 32-bit compilers, but you can still build
 32-bit protoc under 64-bit Windows, with the following command:
 ```
 $ mvn install -Dos.detected.arch=x86_32
@@ -59,10 +73,14 @@ support. DO NOT close the staging repository until you have done the
 deployment for all platforms. Currently the following platforms are supported:
 - Linux (x86_32 and x86_64)
 - Windows (x86_32 and x86_64) with
- - Cygwin with MinGW compilers (both x86_32 and x86_64)
- - MSYS with MinGW32 (x86_32 only)
+ - Cygwin64 with MinGW compilers (x86_64)
+ - MSYS with MinGW32 (x86_32)
 - MacOSX (x86_32 and x86_64)
 
+As for MSYS2/MinGW64 for Windows: protoc will build, but it insists on
+adding a dependency of `libwinpthread-1.dll`, which isn't shipped with
+Windows.
+
 Use the following command to deploy artifacts for the host platform to a
 staging repository.
 ```

protoc-artifacts/build-protoc.sh

@@ -212,7 +212,7 @@ export CXXFLAGS LDFLAGS
 TARGET_FILE=target/protoc.exe
 
 cd "$WORKING_DIR"/.. && ./configure $CONFIGURE_ARGS &&
-  cd src && make clean && make google/protobuf/stubs/pbconfig.h $MAKE_TARGET &&
+  cd src && make clean && make $MAKE_TARGET &&
   cd "$WORKING_DIR" && mkdir -p target &&
   (cp ../src/protoc $TARGET_FILE || cp ../src/protoc.exe $TARGET_FILE) ||
   exit 1