[libc] Disable signal.h API and its users.

The signal.h header file from LLVM libc is incorrect. The signal API and
its users will be enabled once signal.h is fixed.

libc/config/linux/x86_64/entrypoints.txt

@@ -185,21 +185,22 @@ set(TARGET_LIBM_ENTRYPOINTS
 if(LLVM_LIBC_FULL_BUILD)
   list(APPEND TARGET_LIBC_ENTRYPOINTS
     # assert.h entrypoints
-    libc.src.assert.__assert_fail
+    # libc.src.assert.__assert_fail
 
     # stdlib.h entrypoints
     libc.src.stdlib._Exit
-    libc.src.stdlib.abort
+    # libc.src.stdlib.abort
 
     # signal.h entrypoints
-    libc.src.signal.raise
-    libc.src.signal.sigaction
-    libc.src.signal.sigdelset
-    libc.src.signal.sigaddset
-    libc.src.signal.sigemptyset
-    libc.src.signal.sigprocmask
-    libc.src.signal.sigfillset
-    libc.src.signal.signal
+    # TODO: Enable signal.h entrypoints after fixing signal.h
+    # libc.src.signal.raise
+    # libc.src.signal.sigaction
+    # libc.src.signal.sigdelset
+    # libc.src.signal.sigaddset
+    # libc.src.signal.sigemptyset
+    # libc.src.signal.sigprocmask
+    # libc.src.signal.sigfillset
+    # libc.src.signal.signal
 
     # sys/mman.h entrypoints
     libc.src.sys.mman.mmap

libc/src/CMakeLists.txt

@@ -12,8 +12,10 @@ if(NOT LLVM_LIBC_FULL_BUILD)
   return()
 endif()
 
-add_subdirectory(assert)
-add_subdirectory(signal)
+# The signal API is currently disabled as signal.h is incorrect.
+# since assert uses the signal API, we disable assert also.
+# add_subdirectory(assert)
+# add_subdirectory(signal)
 add_subdirectory(stdio)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)

libc/src/stdlib/CMakeLists.txt

@@ -248,14 +248,14 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}._Exit
 )
 
-add_entrypoint_object(
-  abort
-  SRCS
-    abort.cpp
-  HDRS
-    abort.h
-  DEPENDS
-    libc.include.stdlib
-    libc.src.signal.raise
-    ._Exit
-)
+# add_entrypoint_object(
+#   abort
+#   SRCS
+#     abort.cpp
+#   HDRS
+#     abort.h
+#   DEPENDS
+#     libc.include.stdlib
+#     libc.src.signal.raise
+#     ._Exit
+# )

libc/test/src/CMakeLists.txt

@@ -38,8 +38,10 @@ if(NOT LLVM_LIBC_FULL_BUILD)
   return()
 endif()
 
-add_subdirectory(assert)
-add_subdirectory(signal)
+# The signal API is currently disabled as signal.h is incorrect.
+# since assert uses the signal API, we disable assert also.
+# add_subdirectory(assert)
+# add_subdirectory(signal)
 add_subdirectory(stdio)
 add_subdirectory(sys)
 add_subdirectory(threads)

libc/test/src/stdlib/CMakeLists.txt

@@ -125,19 +125,19 @@ add_libc_unittest(
     libc.src.stdlib._Exit
 )
 
-add_libc_unittest(
-  abort_test
-  SUITE
-    libc_stdlib_unittests
-  SRCS
-    abort_test.cpp
-  DEPENDS
-    libc.include.stdlib
-    libc.include.signal
-    libc.src.stdlib.abort
-    libc.src.stdlib._Exit
-    libc.src.signal.raise
-)
+# add_libc_unittest(
+#   abort_test
+#   SUITE
+#     libc_stdlib_unittests
+#   SRCS
+#     abort_test.cpp
+#   DEPENDS
+#     libc.include.stdlib
+#     libc.include.signal
+#     libc.src.stdlib.abort
+#     libc.src.stdlib._Exit
+#     libc.src.signal.raise
+# )
 
 add_libc_unittest(
   abs_test