[libc] Add termios.h and the implementation of functions declared in it.

Reviewed By: lntue, michaelrj

Differential Revision: https://reviews.llvm.org/D136143

Author: Siva Chandra Reddy

libc/config/linux/api.td

@@ -293,3 +293,7 @@ def SysUtsNameAPI : PublicAPI<"sys/utsname.h"> {
 def SpawnAPI : PublicAPI<"spawn.h"> {
   let Types = ["mode_t", "pid_t", "posix_spawnattr_t", "posix_spawn_file_actions_t"];
 }
+
+def TermiosAPI : PublicAPI<"termios.h"> {
+  let Types = ["cc_t", "pid_t", "speed_t", "struct termios", "tcflag_t"];
+}

libc/config/linux/x86_64/entrypoints.txt

@@ -141,6 +141,19 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
 
+    # termios.h entrypoints
+    libc.src.termios.cfgetispeed
+    libc.src.termios.cfgetospeed
+    libc.src.termios.cfsetispeed
+    libc.src.termios.cfsetospeed
+    libc.src.termios.tcgetattr
+    libc.src.termios.tcgetsid
+    libc.src.termios.tcdrain
+    libc.src.termios.tcflow
+    libc.src.termios.tcflush
+    libc.src.termios.tcsendbreak
+    libc.src.termios.tcsetattr
+
     # unistd.h entrypoints
     libc.src.unistd.access
     libc.src.unistd.chdir