Add -fvisibility in Makefile, provide meson example commands.

Shaves off 10 kb in binary. Also -fpic -> -fPIC in Makefile and jpm.

Makefile

@@ -37,7 +37,7 @@ MANPATH?=$(PREFIX)/share/man/man1/
 PKG_CONFIG_PATH?=$(LIBDIR)/pkgconfig
 DEBUGGER=gdb
 
-CFLAGS=-std=c99 -Wall -Wextra -Isrc/include -Isrc/conf -fpic -O2 -fvisibility=hidden \
+CFLAGS=-std=c99 -Wall -Wextra -Isrc/include -Isrc/conf -fPIC -O2 -fvisibility=hidden \
 	   -DJANET_BUILD=$(JANET_BUILD)
 LDFLAGS=-rdynamic
 

README.md

@@ -132,6 +132,25 @@ is maybe more convenient and flexible for integrating into existing pipelines.
 Meson also provides much better IDE integration than Make or batch files, as well as support
 for cross compilation.
 
+For the impatient, building with Meson is as simple as follows. The options provided to
+`meson setup` below emulate Janet's Makefile.
+
+```sh
+git clone https://github.com/janet-lang/janet.git
+cd janet
+meson setup build \
+          --buildtype release \
+          --optimization 2 \
+          -Dgit_hash=$(git log --pretty=format:'%h' -n 1)
+ninja -C build
+
+# Run the binary
+build/janet
+
+# Installation
+ninja -C build install
+```
+
 ## Development
 
 Janet can be hacked on with pretty much any environment you like, but for IDE

auxbin/jpm

@@ -124,7 +124,7 @@
 (def- dynamic-cflags
   (if is-win
     []
-    ["-fpic"]))
+    ["-fPIC"]))
 (def- dynamic-lflags
     (if is-win
       ["/DLL"]

meson.build

@@ -170,15 +170,32 @@ libjanet = library('janet', core_src, core_image,
   dependencies : [m_dep, dl_dep],
   install : true)
 
+# Extra c flags - adding -fvisibility=hidden matches the Makefile and
+# shaves off about 10k on linux x64, likely similar on other platforms.
+native_cc = meson.get_compiler('c', native: true)
+cross_cc = meson.get_compiler('c', native: false)
+if native_cc.has_argument('-fvisibility=hidden')
+  extra_native_cflags = ['-fvisibility=hidden']
+else
+  extra_native_cflags = []
+endif
+if cross_cc.has_argument('-fvisibility=hidden')
+  extra_cross_cflags = ['-fvisibility=hidden']
+else
+  extra_cross_cflags = []
+endif
+
 janet_mainclient = executable('janet', core_src, core_image, init_gen, mainclient_src,
   include_directories : incdir,
   dependencies : [m_dep, dl_dep],
+  c_args : extra_native_cflags,
   install : true)
 
 if meson.is_cross_build()
   janet_nativeclient = executable('janet-native', core_src, core_image, init_gen, mainclient_src,
     include_directories : incdir,
     dependencies : [m_dep, dl_dep],
+    c_args : extra_cross_cflags,
     native : true)
 else
   janet_nativeclient = janet_mainclient