[libc] Add a baremetal config.

[sivachandra]

Summary

The config currently includes ctype, math, stdlib, inttypes and string
functions.

libc/cmake/modules/LLVMLibCArchitectures.cmake

elseif(LIBC_TARGET_ARCHITECTURE STREQUAL "aarch64")
   set(LIBC_LIBC_TARGET_ARCHITECTUREITECTURE_IS_AARCH64 TRUE)
 elseif(LIBC_TARGET_ARCHITECTURE STREQUAL "x86_64")
   set(LIBC_LIBC_TARGET_ARCHITECTUREITECTURE_IS_X86 TRUE)
 else()
   message(FATAL_ERROR
           "Unsupported libc target architecture ${LIBC_TARGET_ARCHITECTURE}")
 endif()
 
+if(LIBC_TARGET_OS STREQUAL "baremetal")
+  set(LIBC_TARGET_OS_IS_BAREMETAL TRUE)
+elseif(LIBC_TARGET_OS STREQUAL "linux")
+  set(LIBC_TARGET_OS_IS_LINUX TRUE)
+elseif(LIBC_TARGET_OS STREQUAL "darwin")
+  set(LIBC_TARGET_OS_IS_DARWIN TRUE)
+elseif(LIBC_TARGET_OS STREQUAL "windows")
+  set(LIBC_TARGET_OS_IS_WINDOWS TRUE)
+else()
+  message(FATAL_ERROR
+          "Unsupported libc target operating system ${LIBC_TARGET_OS}")
+endif()
+
+
 # If the compiler target triple is not the same as the triple specified by
 # LIBC_TARGET_TRIPLE, we will add a --target option if the compiler is clang.
 # If the compiler is GCC we just error out as there is no equivalent of an
 # option like --target.
 if(LIBC_TARGET_TRIPLE AND
    (NOT (libc_compiler_triple STREQUAL LIBC_TARGET_TRIPLE)))
   if(CMAKE_COMPILER_IS_GNUCXX)
     message(FATAL_ERROR
             "GCC target triple and LIBC_TARGET_TRIPLE do not match.")
   else()
     list(APPEND LIBC_COMPILE_OPTIONS_DEFAULT "--target=${LIBC_TARGET_TRIPLE}")
   endif()
 endif()
 
 message(STATUS
         "Building libc for ${LIBC_TARGET_ARCHITECTURE} on ${LIBC_TARGET_OS}")

libc/config/baremetal/api.td

+include "config/public_api.td"
+
+include "spec/stdc.td"
+
+def CTypeAPI : PublicAPI<"ctype.h"> {
+}
+
+def IntTypesAPI : PublicAPI<"inttypes.h"> {
+  let Types = ["imaxdiv_t"];
+}
+
+def StdlibAPI : PublicAPI<"stdlib.h"> {
+  let Types = [
+    "div_t",
+    "ldiv_t",
+    "lldiv_t",
+    "size_t",
+    "__bsearchcompare_t",
+    "__qsortcompare_t",
+    "__atexithandler_t",
+  ];
+}
+
+def StringAPI : PublicAPI<"string.h"> {
+  let Types = ["size_t"];
+}

libc/config/baremetal/entrypoints.txt

+set(TARGET_LIBC_ENTRYPOINTS
+    # ctype.h entrypoints
+    libc.src.ctype.isalnum
+    libc.src.ctype.isalpha
+    libc.src.ctype.isascii
+    libc.src.ctype.isblank
+    libc.src.ctype.iscntrl
+    libc.src.ctype.isdigit
+    libc.src.ctype.isgraph
+    libc.src.ctype.islower
+    libc.src.ctype.isprint
+    libc.src.ctype.ispunct
+    libc.src.ctype.isspace
+    libc.src.ctype.isupper
+    libc.src.ctype.isxdigit
+    libc.src.ctype.toascii
+    libc.src.ctype.tolower
+    libc.src.ctype.toupper
+
+    # string.h entrypoints
+    libc.src.string.bcmp
+    libc.src.string.bcopy
+    libc.src.string.bzero
+    libc.src.string.memccpy
+    libc.src.string.memchr
+    libc.src.string.memcmp
+    libc.src.string.memcpy
+    libc.src.string.memmove
+    libc.src.string.mempcpy
+    libc.src.string.memrchr
+    libc.src.string.memset
+    libc.src.string.stpcpy
+    libc.src.string.stpncpy
+    libc.src.string.strcat
+    libc.src.string.strchr
+    libc.src.string.strcmp
+    libc.src.string.strcpy
+    libc.src.string.strcspn
+    libc.src.string.strlcat
+    libc.src.string.strlcpy
+    libc.src.string.strlen
+    libc.src.string.strncat
+    libc.src.string.strncmp
+    libc.src.string.strncpy
+    libc.src.string.strnlen
+    libc.src.string.strpbrk
+    libc.src.string.strrchr
+    libc.src.string.strspn
+    libc.src.string.strstr
+    libc.src.string.strtok
+    libc.src.string.strtok_r
+
+    # inttypes.h entrypoints
+    libc.src.inttypes.imaxabs
+    libc.src.inttypes.imaxdiv
+    libc.src.inttypes.strtoimax
+    libc.src.inttypes.strtoumax
+ 
+    # stdlib.h entrypoints
+    libc.src.stdlib.abs
+    libc.src.stdlib.atoi
+    libc.src.stdlib.atof
+    libc.src.stdlib.atol
+    libc.src.stdlib.atoll
+    libc.src.stdlib.bsearch
+    libc.src.stdlib.div
+    libc.src.stdlib.labs
+    libc.src.stdlib.ldiv
+    libc.src.stdlib.llabs
+    libc.src.stdlib.lldiv
+    libc.src.stdlib.qsort
+    libc.src.stdlib.strtod
+    libc.src.stdlib.strtof
+    libc.src.stdlib.strtol
+    libc.src.stdlib.strtold
+    libc.src.stdlib.strtoll
+    libc.src.stdlib.strtoul
+    libc.src.stdlib.strtoull
+)
+
+set(TARGET_LIBM_ENTRYPOINTS
+    # math.h entrypoints
+    libc.src.math.fabs
+    libc.src.math.fabsf
+    libc.src.math.fabsl
+    libc.src.math.fdim
+    libc.src.math.fdimf
+    libc.src.math.fdiml
+    libc.src.math.fmax
+    libc.src.math.fmaxf
+    libc.src.math.fmaxl
+    libc.src.math.fmin
+    libc.src.math.fminf
+    libc.src.math.fminl
+)
+
+set(TARGET_LLVMLIBC_ENTRYPOINTS
+  ${TARGET_LIBC_ENTRYPOINTS}
+  ${TARGET_LIBM_ENTRYPOINTS}
+)

libc/config/baremetal/headers.txt

+set(TARGET_PUBLIC_HEADERS
+    libc.include.ctype
+    libc.include.errno
+    libc.include.inttypes
+    libc.include.math
+    libc.include.stdlib
+    libc.include.string
+)

libc/test/utils/tools/WrapperGen/CMakeLists.txt

+if(LIBC_TARGET_OS_IS_BAREMETAL)
+  return()
+endif()
+
 add_libc_tool_unittest(
   wrappergen_test
   SRCS 
     wrappergen_test.cpp   
   ARGS
     --path=${LIBC_SOURCE_DIR}
     --tool=${LLVM_BINARY_DIR}/bin/libc-wrappergen
     --api=${LIBC_SOURCE_DIR}/test/utils/tools/WrapperGen/testapi.td
 )
 
 add_dependencies(wrappergen_test libc-wrappergen)

libc/utils/CMakeLists.txt

 add_subdirectory(MPFRWrapper)
 add_subdirectory(testutils)
 add_subdirectory(UnitTest)
 
-if(LLVM_LIBC_FULL_BUILD AND NOT LIBC_TARGET_ARCHITECTURE_IS_GPU)
+if(LLVM_LIBC_FULL_BUILD AND NOT
+  (LIBC_TARGET_ARCHITECTURE_IS_GPU OR LIBC_TARGET_OS_IS_BAREMETAL))
   add_subdirectory(IntegrationTest)
   add_subdirectory(tools)
 endif()