[PATCH] INSTALL: add macOS gettext and sdk header explanation to INSTALL

@@ -165,6 +165,9 @@ Issues of note:
 	  use English. Under autoconf the configure script will do this
 	  automatically if it can't find libintl on the system.
 
+    In macOS, can install and link gettext with brew as "brew install gettext"
+    and "brew link --force gettext", the link operation is necessary.
+
 	- Python version 2.4 or later (but not 3.x, which is not
 	  supported by Perforce) is needed to use the git-p4 interface
 	  to Perforce.

@@ -178,6 +181,10 @@ Issues of note:
    will include them.  Note that config.mak is not distributed;
    the name is reserved for local settings.
 
+  - In macOs 10.14, the Command Line Tool not contains the headers as before, so it
+    need install Command Line Tool 10.14 and install the headers which command
+    "sudo installer -pkg /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg -target".
+
  - To build and install documentation suite, you need to have
    the asciidoc/xmlto toolchain.  Because not many people are
    inclined to install the tools, the default build target