Add picolibc support [v2]

This adds support for using picolibc instead of newlib on embedded
systems.

Signed-off-by: Keith Packard <keithp@keithp.com>

v2:
	Add check for meson and ninja
	Sync option default values with current picolibc defaults
	Remove xtensa sys header file install as those aren't in picolibc

1 files changed, 124 insertions, 0 deletions

diff --git a/config/libc/picolibc.in b/config/libc/picolibc.in
new file mode 100644
index 00000000..cc1d4d1f
--- /dev/null
+++ b/config/libc/picolibc.in
@@ -0,0 +1,124 @@
+# picolibc options
+
+## depends on BARE_METAL && CONFIGURE_has_meson && CONFIGURE_has_ninja
+## select LIBC_SUPPORT_THREADS_NATIVE
+
+## select CC_CORE_PASSES_NEEDED if CANADIAN
+## select CC_CORE_PASS_2_NEEDED if ! CANADIAN
+
+## help Picolibc is a C library intended for use on embedded systems. It is a
+## help conglomeration of several library parts, all under BSD-compatible software
+## help licenses that make them easily usable on embedded products. Picolibc
+## help is only available in source form. It can be compiled for a wide
+## help array of processors, and will usually work on any architecture with
+## help the addition of a few low-level routines.
+
+config PICOLIBC_CXA_ATEXIT
+    def_bool y
+    select LIBC_PROVIDES_CXA_ATEXIT
+
+config LIBC_PICOLIBC_TARGET_CFLAGS
+    string
+    prompt "Target CFLAGS for picolibc"
+    default ""
+    help
+      Used to add specific options when compiling the target libraries
+      (eg. -ffunction-sections -fdata-sections), which can't be defined
+      in global TARGET_CFLAGS, because they shall be not used for the
+      gcc target libraries.
+      Note:  Both TARGET_CFLAGS and LIBC_PICOLIBC_TARGET_CFLAGS are used
+             to compile the libraries.
+
+      Leave blank if you don't know better.
+
+config LIBC_PICOLIBC_IO_C99FMT
+    bool
+    prompt "Enable IOs on C99 formats"
+    default y
+    help
+      Enable support for IOs on C99 formats.
+
+config LIBC_PICOLIBC_REGISTER_FINI
+    bool
+    prompt "Enable finalization function registration using atexit"
+    help
+        Enable finalization function registration using atexit.
+
+config LIBC_PICOLIBC_ATEXIT_DYNAMIC_ALLOC
+    bool
+    prompt "Enable dynamic allocation of atexit entries"
+    help
+        Enable dynamic allocation of atexit entries.
+
+config LIBC_PICOLIBC_GLOBAL_ATEXIT
+    bool
+    prompt "Enable atexit data structure as global variable"
+    help
+        Enable atexit data structure as global variable, instead
+	of being thread-local.
+
+config LIBC_PICOLIBC_LITE_EXIT
+    bool
+    prompt "Enable lite exit"
+    default y
+    help
+        Enable lite exit, a size-reduced implementation of exit that doesn't
+        invoke clean-up functions such as _fini or global destructors.
+
+config LIBC_PICOLIBC_MULTITHREAD
+    bool
+    prompt "Enable support for multiple threads"
+    default y
+    help
+        Enable support for multiple threads.
+
+config LIBC_PICOLIBC_RETARGETABLE_LOCKING
+    bool
+    prompt "Enable retargetable locking"
+    help
+        Enable retargetable locking to allow the operating system to override
+        the dummy lock functions defined within picolibc.
+
+config LIBC_PICOLIBC_EXTRA_SECTIONS
+    bool
+    prompt "Place each function & data element in their own section"
+    help
+        Place each function & data symbol in their own section. This allows
+        the linker to garbage collect unused symbols at link time.
+
+config LIBC_PICOLIBC_ENABLE_TARGET_OPTSPACE
+    bool
+    prompt "Optimize picolibc for size"
+    default y
+    help
+      Pass --enable-target-optspace to picolibc configure.
+
+      This will compile picolibc with -Os.
+
+config LIBC_PICOLIBC_LTO
+    bool
+    prompt "Enable Link Time Optimization"
+    depends on CC_GCC_USE_LTO
+    help
+      Builds the libraries with -flto to enable more aggressive link time
+      optimization. You will need to add -flto-partition=one to your
+      application's link line to keep the RETURN assembler macro together
+      with it's consumers.
+
+config LIBC_PICOLIBC_NANO_MALLOC
+    bool
+    prompt "Enable Nano Malloc"
+    default y
+    help
+      PICOLIBC has two implementations of malloc family's functions, one in
+      `mallocr.c' and the other one in `nano-mallocr.c'.  This options
+      enables the nano-malloc implementation, which is for small systems
+      with very limited memory.  Note that this implementation does not
+      support `--enable-malloc-debugging' any more.
+
+config LIBC_PICOLIBC_EXTRA_CONFIG_ARRAY
+    string
+    prompt "Extra config for picolibc"
+    default ""
+    help
+      Extra flags to pass to meson when configuring picolibc.