docs: instructions on how to compile selected architectures

docs/COMPILE-NIX.md

@@ -22,12 +22,27 @@ CMake is required to build keystone.
         $ cd build
         $ ../make-share.sh
 
+   By default, this builds all architectures, which is: AArch64, ARM, Hexagon,
+   Mips, PowerPC, Sparc, SystemZ & X86. To compile just some selected ones,
+   pass a semicolon-separated list of targets to LLVM_TARGETS_TO_BUILD,
+   like follows if we only want AArch64 & X86.
+
+        $ cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=ON -DLLVM_TARGETS_TO_BUILD="AArch64, X86" -G "Unix Makefiles" ..
+        $ make -j8
+
    You can also compile static a library with:
 
         $ mkdir build
         $ cd build
         $ ../make-lib.sh
 
+   Like above, this builds all architectures. To compile just some selected ones,
+   pass a semicolon-separated list of targets to LLVM_TARGETS_TO_BUILD,
+   like follows if we only want AArch64 & X86.
+
+        $ cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=OFF -DLLVM_TARGETS_TO_BUILD="AArch64, X86" -G "Unix Makefiles" ..
+        $ make -j8
+
 
 2. Right after building, install Keystone.
 

docs/COMPILE-WINDOWS.md

@@ -21,10 +21,25 @@ https://www.visualstudio.com
 
         $ ..\nmake-dll.bat
 
+   By default, this builds all architectures, which is: AArch64, ARM, Hexagon,
+   Mips, PowerPC, Sparc, SystemZ & X86. To compile just some selected ones,
+   pass a semicolon-separated list of targets to LLVM_TARGETS_TO_BUILD,
+   like follows if we only want AArch64 & X86.
+
+        $ cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=ON -DLLVM_TARGETS_TO_BUILD="AArch64, X86" -G "NMake Makefiles" ..
+        $ nmake
+
   To build LIB file, run:
 
         $ ..\nmake-lib.bat
 
+   Like above, this builds all architectures. To compile just some selected ones,
+   pass a semicolon-separated list of targets to LLVM_TARGETS_TO_BUILD,
+   like follows if we only want AArch64 & X86.
+
+        $ cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=OFF -DLLVM_TARGETS_TO_BUILD="AArch64, X86" -G "NMake Makefiles" ..
+        $ nmake
+
   Find the generated libraries in build\llvm\lib\keystone.{dll,lib}
   
   In the case you build LIB file, a tool named "kstool.exe" is also