Add support for the loading of ET_DYN objects

* libs/libc/machine/arm/armv7-m/arch_elf.c
      - Fix cast of error message parameters

    * build-globals.sh
      - Build the modlib_globals.S file used to resolve symbols when dynamically loading

    * libs/libc/modlib/Make.defs
      - Build modlib_globals.S for all targets

    * libs/libc/modlib/modlib_load.c
      - Calculate sizes and text/data addresses based on program headers rather than section headers
      - Handle objects with no program headers

    * libs/libc/modlib/modlib_bind.c
      - Call modlib_readsym with pointer to symbol table
      - Add modlib_relocatedyn to manage relocation of symbols with shared object (ET_DYN)
      - Differentiate between ET_REL and ET_DYN objects
      - Use arch independent symbol ELF_R_SYM
      - Cast sizes to avoid warnings

    * libs/libc/modlib/modlib_load.c
      - Cast sizes to avoid warnings

    * include/elf.h
      - Add definitions that may be found in shared objects

    * include/nuttx/lib/modlib.h
      - Add parameter to modlib_readsym prototype
      - Add prototypes for:
        - modlib_insertsymtab
        - modlib_findglobal
      - Define Elf_Dyn and Elf_Off according to the elf architecture
      - Add fields to mod_loadifno_s:
        - Program headers
        - Exported symbols
        - Data section address
        - Padding requirement
        - Section index for dynamic symbol table
        - Number of symbols exported
      - Add prottotype for modlib_freesymtab

    * libs/libc/dlfcn/lib_dlclose.c
      - Free the symbol table when the dll is closed

    * libs/libc/dlfcn/lib_dlopen.c
      - Add dump of program headers to debug routine
      - Differentiate between ET_REL and ET_DYN objects

    * libs/libc/machine/arm/armv7-m/arch_elf.c
      - Add handling of R_ARM_RELATIVE and R_ARM_JUMP slot relocation types

    * libs/libc/modlib/modlib_loadshdrs.c
      - Rename modlib_loadshdrs.c to modlib_loadhdrs.c
      - Rename modlib_loadshdrs to modlib_loadhdrs
      - Add code to load program headers

    * libs/libc/modlib/modlib_symbols.c
      - Define entry point structure
      - Add offset parameter to modlib_symname() and use to find symbol names
      - Add symtab section header parameter to modlib_readsym()
      - Add offset parameter to modlib_symvalue() to locate symbol names
      - Add modlib_insertsyntab() to create a symbol table for exporting and resolution
      - Add findEP() to resolve a symbol in the modlib_global table
      - Add modlib_findglobal() to find symbol in the modlib_global table
      - Add modlib_freesymtab() to free the symbol table

    * libs/libc/modlib/modlib_uninit.c
      - Free header and sections from a module_loadinfo_s control block

    * libs/libc/modlib/modlib_verify.c
      - Handle ET_DYN shared objects

    * libs/libc/modlib/modlib_globals.S
      - Multi-target global table
      - Define library APIs that may be resolved when loading a shared object

include/elf.h

@@ -214,6 +214,17 @@
 #define PT_NOTE            4
 #define PT_SHLIB           5
 #define PT_PHDR            6
+
+/* Processor specific values for the Phdr p_type field.  */
+
+#define PT_ARM_EXIDX            (PT_LOPROC + 1) /* ARM unwind segment.  */
+
+/* GCC specific */
+
+#define PT_GNU_EH_FRAME 0x6474e550      /* GCC exception handler frame */
+#define PT_GNU_STACK    0x6474e551      /* Stack executability */
+#define PT_GNU_RELRO    0x6474e552      /* Read-only after relocation */
+
 #define PT_LOPROC          0x70000000
 #define PT_HIPROC          0x7fffffff