Check for and use no-undefined linker flag, explicitly link with libc

Check if the linker can link with '-Wl,--no-undefined' and apply the flag
when linking libbstring

Also for the sake of OpenBSD, look for and explicitly link with libc
in order to address the linker error that the above flag revealed

Author: rdmark

bstring/meson.build

@@ -6,6 +6,8 @@ libbstring = library(
     version: '1.0.0',
     soversion: '1',
     include_directories: bstring_inc,
+    dependencies: bstring_deps,
+    link_args: linker_flags,
     install: true,
 )
 

meson.build

@@ -10,6 +10,18 @@ add_project_arguments('-fno-common', language: 'c')
 add_project_arguments('-fvisibility=hidden', language: 'c')
 
 bstring_inc = include_directories(['.', 'bstring'])
+bstring_deps = []
+libc_dep = cc.find_library('c', required: false)
+
+if libc_dep.found()
+    bstring_deps += [libc_dep]
+endif
+
+linker_flags = []
+
+if cc.has_link_argument('-Wl,--no-undefined')
+    linker_flags = ['-Wl,--no-undefined']
+endif
 
 bgets_test_code = '''
 #include <stdio.h>