[ELF/LinkerScript] Support PROVIDE/PROVIDE_HIDDEN inside output sections description.

[davide]

Summary

Reference: https://svnweb.freebsd.org/base/head/sys/conf/ldscript.amd64?revision=284870&view=markup#l97

[ruiu]

LGTM

lld/trunk/ELF/LinkerScript.cpp

if (Tok == "*") {
       expect("(");
       auto *InCmd = new InputSectionDescription();
       Cmd->Commands.emplace_back(InCmd);
       while (!Error && !skip(")")) {
         Opt.KeptSections.push_back(peek());
         InCmd->Patterns.push_back(next());
       }
       expect(")");
+    } else if (Tok == "PROVIDE") {
+      readProvide(false);
+    } else if (Tok == "PROVIDE_HIDDEN") {
+      readProvide(true);
     } else {
       setError("unknown command " + Tok);
     }
   }
   Cmd->Phdrs = readOutputSectionPhdrs();
 
   StringRef Tok = peek();
   if (Tok.startswith("=")) {

lld/trunk/test/ELF/linkerscript-provide-in-section.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo \
+# RUN: "SECTIONS { . = 1000; .blah : { PROVIDE(foo = .); } }" \
+# RUN:   > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t -shared
+# RUN: llvm-objdump -t %t1 | FileCheck %s
+# CHECK: 00000000000003e8         *ABS*           00000000 foo
+
+# RUN: echo \
+# RUN: "SECTIONS { . = 1000; .blah : { PROVIDE_HIDDEN(foo = .); } }" \
+# RUN:   > %t2.script
+# RUN: ld.lld -o %t2 --script %t2.script %t -shared
+# RUN: llvm-objdump -t %t2 | FileCheck %s --check-prefix=HIDDEN
+# HIDDEN: 00000000000003e8         *ABS*           00000000 .hidden foo
+
+.section blah
+.globl patatino
+patatino:
+  movl $foo, %edx